And what does this do safety/privacy-wise?
Nothing, except make it more available.
This is why I often argue against (or at least want to point out the dangers of) the ATProto/Bluesky model.
It's an absolute boon for people who want heavy surveillance, government or otherwise.
The looseness and "unreliability" of protocols like Mastodon ironically make them safer.
I am genuinely confused. Isn't the point of public social media to be... public? Or do you use BlueSky to talk to your friends, instead of Signal?
Yes, AT proto is about making data available to the public via replication. There's no privacy at all, but it's useful for some things. Hacker News comments don't have any privacy either.
There's another protocol in the works that should be useful for syncing private data:
https://github.com/bluesky-social/proposals/pull/94