Not OP, but threading. So many collaboration tools I've worked with are indistinguishable from the comment section of a blog or newspaper. The vast majority of the comments are useless, with people arguing over ridiculous things, but there's no natural segregation of useful comments and useless, so all you can do is scroll about hope to encounter something worth while.
Well, I only have experience with chat apps, but I think it's the advantages of chat (rooms/subs basically for teas + private messages), but without the expectation of immediate feedback. Also probably great searchability.