[tabbott]

The point is that it's a lot faster to process 20 unread threads with 100 messages than 100 unread messages, because they're nicely grouped. E.g. you can skip reading the 30 messages in the thread about "afternoon lunch", without having to look at those messages (as you would with slack if you wanted to find out that the 'annual meeting' announcement happened).

For diverging topics, you can easily edit the topics of the messages that are a diversion to be a new topic. This helps a huge amount when you have new users who haven't learned the convention of creating a new topic when bringing up something unrelated, since anyone can clean it up in a few seconds.