Chat systems are for rapid typing -- constant flow of communication.

Bbc/email systems are for long-form communications -- slow, methodical and referencable.

Slack and its friends committed the great crime of conflating the two, to produce systems that are never as quick as you'd like, and never as referencable as you'd like, and no one knows how to effectively communicate on it because there is no effective communication unless all parties forcibly drop back to irc