the point is not to encrypt your user id, check this out if you haven't seen it I think I explain it better here: https://lemmyadmin.site/comment/46. It's a lot more privacy. And thinking as an admin that wants to provide a safe space for my users, I think it's worth the effort. I took a very quick look at the tables related to person and I'd bet you could treat these similarly to community_follower:
TABLE "comment_like" CONSTRAINT "comment_like_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "comment_saved" CONSTRAINT "comment_saved_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "community_block" CONSTRAINT "community_block_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "community_follower" CONSTRAINT "community_follower_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "person_follower" CONSTRAINT "person_follower_follower_id_fkey" FOREIGN KEY (follower_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "post_like" CONSTRAINT "post_like_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "post_read" CONSTRAINT "post_read_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "post_saved" CONSTRAINT "post_saved_person_id_fkey" FOREIGN KEY (person_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "private_message" CONSTRAINT "private_message_creator_id_fkey" FOREIGN KEY (creator_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
TABLE "private_message" CONSTRAINT "private_message_recipient_id_fkey" FOREIGN KEY (recipient_id) REFERENCES person(id) ON UPDATE CASCADE ON DELETE CASCADE
so consider a smaller local instance like I'm setting up. If it's ever anything more than me and my mom it's gonna be a bunch of people I know and their friends. And if my instance is their entry point to the fediverse then yeah I want it to be as private as we can make it for them.
But also, even if someone's IRL identity was masked, I've only been around a week and I'm starting to recognize handles on the fediverse. Ideally we make friends here and it's a community for us.
Now imagine how humiliating it would be if someone malicious gained control over an instance and published everyone's subscriptions/likes etc. Sure more savvy users probably do have separate accounts but honestly most will not.