+1. Also, chats imply a semi-synchronous conversation, which IMHO is the worst of both worlds. Talking to people 1:1 is disruptive, but at least very efficient. E-mails are slow, but very non-disruptive. Chats are slow, inefficient _and_ almost as disruptive as talking.

You could use them in an async manner I guess, but Slack isn't really made for that, it's clumsy as an e-mail replacement.