I've used both kinds of forums, and I think both trees and linear threads - let's call them 'streams' - have their places. If you imagine a forum as a large

I've used both kinds of forums, and I think both trees and linear threads - let's call them 'streams' - have their places. If you imagine a forum as a large dinner table, trees are like conversations that start out at one corner of the table, maybe with a few people participating, and then usually split off into individual exchanges that don't interact with each other. When that happens late in the dinner after coffee and liquor, people usually move around and form little groups. Streams are like shared conversations involving the entire table - one person at a time talks, everybody listens and replies. Sometimes people try to talk over each other, sometimes it's mostly two or three people talking and the others are nodding along for a while. But it's what makes the experience a communal one, and it's how you get to know the people in the group other than the few you directly spoke to. It also acts as a moderating influence, since if two people are getting into a heated debate over some niche issue, other attendees will usually try to mediate for the sake of the event, instead of ignoring them and letting them fight among them. Stream-based forums IME tended to form more robust communities where people recognized each other's names and avatars, whereas even in smaller subreddits I might recognize a couple of very frequent commenters but nowhere near as easily or as often. On the other side, tree-based forums make it much easier to establish a rapport with the couple of people you wanted to talk to and ignore everybody else. (Potential objection: nothing's stopping a tree system from acting like a stream by having a "main" thread where most everybody pipes up. In theory that's true, but in practice I find that threads simply don't have the staying power of streams, because they fade off into the 'click here for the next 20 replies' purgatory where only the participants and a few lurkers follow. Streams keep all the eyeballs in the same place.)