Board Thread:General Discussion/@comment-24510587-20171210195728/@comment-24510587-20171210232209

Not everyone has everyone in their friend list. And besides, having everything in one place is better than having a number of scattered group DMs.

Turning off mentions in a channel or server mutes any and all mentions, even the ones that might concern you. In this shape, people can easily and quickly mention only the group of people they're referring to.

It doesn't clutter at all, as people will only be able to see the channels for which they have the appropriate roles.

TL;DR: Group DMs do not substitute.