It's important though because it allows you to communicate things that don't really belong in the open while remaining under your identity on that platform and avoiding the need to link that identity with your identity on a different service.
It would be useful if I could send people Signal link where they could login with their Facebook/Google/Instagram account (OIDC) to chat with me over Signal.
Signal no longer requires phone numbers as identifiers, so this might be feasible.
The thing is that a closed system like DMs on a platform can be more effectively monitored for spam than something like email (or phone calls or texts) because everything is under single control.
