It’s not a bad thing. People on there, if you piss them off in a discussion, will go find your old posts and downvote them and in some rare cases harass you by replying or worse put two and two together to doxx you.
Eh, for investigating scammers/bots it's a real pain in the ass.
Massive changes in posting history was a very good sign that an account was a farmed or stolen account.
Makes it a lot easier for reddit to deny their bot problem.
Not sure what you mean. They can still do all that even if the profile is set to private. It doesn't hide your posts and comments from Google. They are hoovered up just the same.