If you can subscribe to communities on other instances than the one you're registered with, why register on one vs another?

https://lemmy.world/post/52249

If you can subscribe to communities on other instances than the one you're registered with, why register on one vs another? - Lemmy.world

I am new and trying to understand how Lemmy works. I am posting this from my lemmy.world account, on a lemmy.ml [http://lemmy.ml] community. It seems like you can read, post, subscribe to whatever community outside of the instance you’re registered with. So… Why register on lemmy.world vs lemmy.ml [http://lemmy.ml] or any other instance, if all communities are accessible to everyone?

Rules. Community feel. Performance. Geographic location. Just off the top of my head.
what about jurisdiction? is that a factor?
Could I, an EU citizen, say, I really want to extra failsafe and benefits of GDPR by signing up on an instance based in an EU country, with a server inside an EU country, abiding EU laws and standard of privacy protection? Is that a thing? Or is the lemmy ecosystem a lawless wild west?
Currently... all very new and I'd say more like the latter. I'm not a lawyer, but I assume GDPR has exemptions for non-business ventures?
As far as I know the exceptions are only for personal use (whatever that means)