tl;dr
On a small scale reciprocal following is fine. As the audience grows some kind of single follow keeps the platform usable for creators. Multiple follow helps creators to publish different topics without annoying their audience. Once there are many users some kind of topic following in combination with voting and an algorithm works best.
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Or: Why reddit got the best follow model for large networks
Social platforms enable their users to connect with others. To do so they use different models. Most of them are broken because the usage of the platform changed over time. Some more, some less. I take a look at the different models and explain what I believe they do well and where they fail.
Old media subscription

In the dead wood world it was easy. There were publishers and recipients. You could buy a magazine, watch a show or listen to a station. Or not. The publishers bundled their stuff and in most cases it was quite clear what you were getting. If you dig a bit deeper it isn’t that easy anymore because journalist worked for different publishers. But as a recipient that wasn’t important for you. In most cases you got the end-product as a whole thing.
Creator -> Publisher (Editor) -> Recipient
If you liked something you subscribed to it to get it regularly. Because of the publisher you knew what you were getting and it only changed very slowly if at all.
Single follow: subscription

Made popular by Twitter. It is very similar to the old media subscription with the main difference that the Editor got removed and you follow the creator directly, who is also the publisher. Everyone can be a publisher now. This fits to the 90-9-1 principle. One person creates something, nine interact with it and ninety consume silently. For the participators there is often some kind of back channel. Like comments on blogs or youtube and replies on Twitter.
Creator -> Recipient
The great thing about the model: It can be reciprocal but doesn’t have to. This is important for creators to reach many people while only following those they like to consume instead of being forced to consume the noise of everyone who listens to them.
Problems arise when people write about different topic or even in different languages. As a result people create multiple accounts for different topics and languages. That means that followers don’t get everything anymore or creators have to write several updates to reach everyone which may annoy those who follow more than one account.
Reciprocal follow: “friends”

Most popular. MySpace, Facebook and many others. Both parties have to say yes to get each others updates. Or stay in contact. Works ok for friendships and contacts. Problem is that these are much more agile than the model can represent. I may be close with someone but I am neither interested in what they do for work nor most of their hobbies. The subset of people from whom I want to get every bit of information is small. For me it’s 30 people and I got them on Path.
Facebook used to be similar. It was for friends. But as it grew this changed. They recognized that it doesn’t work well for the recipient to get all updates from everyone they are connected to. Their first solution was the edgerank. An algorithm that tries to only show the updates that are most interesting for the user. It uses different data to achieve it. How often one interacts with someone, how many other people interact with a certain update, what kind of update it is and how this kind of update got interaction from the user in the past. And many more. Their second solution was the implementation of a single follow model in addition to the reciprocal follow. People can now subscribe to someone if the user has enabled it without being a friend. They already had the single follow for pages. The third solution is interest lists to bundle people and pages into new feeds because the edge rank doesn’t work for everyone. Especially lurkers have a hard time because of their non interaction. This three things show how bad the reciprocal follow works on a bigger scale.
Creator+Recipient <-> Creator+Recipient
No creator wants to consume everything their recipients produce. The same problems as with single follow exist.
Selected recipients and sorted publishers: Lists

This is what google+ does with circles and Facebook with lists. Reducing visibility to a group selected by the creator. In my opinion it’s fucked up. The publisher sorts its recipients into groups. This works if used for privacy but not for topics. I have no clue what my followers on Facebook/Google+ are interested in. I don’t want to sort them into groups and give each of them different messages.
The same groups are used to follow people. Even more fucked up. Now I have to say what others are writing about and why I am interested in them. But it does change in any way what I get to read by them because they need to sort me into the right group so I get the right updates. This doesn’t work.
Example: I put someone in the ‘startup’ circle to only send them updates about startups. They put me in the ‘video games’ circle because they read an article about this topic by me. I now spam their gaming stream with startup news and they never get my gaming updates because I didn’t put them into that circle.
With public circles it got slightly better because people at least know what I think they are interested in. Now circles are similar to Facebooks groups where people can join because of the topic and post and receive everything about it. But this is removed from the normal following and more similar to a classic forum.
Twitter also added sorted publishers in form of lists as people had a hard time follow all updates. This is bad because it forces people to be single topic.
O -> O
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<-O
Selected recipients are a bad idea. The creators don’t know their audience that well and the audience isn’t that got at sorting creators into groups. Mixing both things is even worse.
Multiple follow: Several categories by one person

Made popular by Pinterest. I think it is one of the best. The publisher sorts its content into groups. These can be topical or privacy or something else. And the follower can say in which groups they are interested in. Or if they want to get everything and follow the person itself which automatically subscribes them to all groups. Past and future.
The only problem are updates that fit into several groups. It could make sense to enable the publisher to add meta updates that all subscribers get, no matter if they follow only one group or all.
This is similar to tagging or categories of blogs. But I believe that exclusive topics are more powerful. Also the follow mechanism on Pinterest is way easier than adding different RSS feeds from a blog to a feedreader. With a blog new categories and topics are added all the time because the publisher doesn’t think of them as the main follow model. People read the blog. As a consequence bloggers often believe they have to only cover a certain set of topics. Else people will unsubscribe. That’s right. Because the prominent single follow model of blogs doesn’t fit into today’s media creation and consumption.
Creator -> Topic 1
Creator -> Topic 2 -> Recipient 1
Creator -> Topic 3 -> Recipient 2
This is great for curation and allows the creator to publish a variety of stuff while the recipients choose which topics they are interested in.
Topic follow: Multiple categories by multiple persons

Reddit also uses the multiple follow model. In my eyes even better than pinterest. You can single follow people, they are then called friends even though it’s not reciprocal. But the great thing is: You can follow subreddits with topics that interest you. Instead of a edgerank there are up and downvotes that feed an algorithm to show what’s most interesting in a certain topic. Alternatively you can look at new submissions, controversial or top. Your front page is now populated with interesting submissions from all topics that interest you. You can visit a subreddit to only show submissions of a certain topic or even create another account to bundle a different set of topics. Creators choose the right topic for their submission and you don’t even have to follow them directly. Thanks to the voting you still get only the best stuff. As a creator you can reach a large audience even if nobody has ever heard from you before.
This is also used by Quora where people follow topics and/or people.
Creator -> topic -> recipients
Topic follow removes the need to follow people and therefore enables creators to be as multi dimensional as they want.
Conclusions about different platforms
Google+s Circles are fucked up. They don’t work. Wrong direction. Double blind. The publisher sorts people into circles he thinks they might be interested. The recipient sorts publishers into circles he thinks they write about.
When Facebook was a network of your college friends the reciprocal model worked fine. But then other groups got added and they added layers of privacy through networks and later lists. The lists try to be like circles and don’t work for the same reasons.
Twitter once had a simple single follow model. But then introduced lists which don’t work because the sorting is done by the wrong side. Readers are only good at sorting when the publisher is one-dimensional. Again. Most people aren’t. Especially the ones I enjoy reading. With hashtags they got some kind of topic follow model but because of spam and low quality content it doesn’t work well.
Pinterest got it right by letting the publisher say what they are publishing and the recipient decide what they are interested in. The reader doesn’t have to look at a circle or list to get the right content but gets the mix in their main feed. They then can sort interesting content by their own sorting system. Curation at its best. But it would work nice for publishing too.
Quora, one of my big loves at the moment, also uses a multiple follow model. But they added some complexity by adding a new type of content. They now have questions and posts. I can follow topics, people, boards and single questions. The publisher can say into which topics the content fits, the recipient in which they are interested. And as a bonus they can change the topics if they think they are wrongly used. All gets mixed by an algorithm for the main feed.
Reddit, my other love, uses a combined multiple (subreddits) and single (users) follow model too. It is less complex and has better options to consume content. The creator is less important than the content.