We have Lemmy.world, Lemmy.ml, beehaw.org, I think even yiffit.net. If I log in using wefwef it asks me where I want to login. And when I make a new account using another instance, it says ”… Lemmy is federated, so you can interact with everything on lemmy.ml even if you’re registered on a different instance.“ So if I’m registered on lemmy.world, how can I interact with lemmy.ml?
On top of what other people have already said each instance has different rules. One instance might have rules against NSFW content and defederate from NSFW instances while others may be fine with it.
And you can have multiple accounts. One on non-nsfw side, and one on nsfw side. Then add both accounts to your favorite client. This way you have clean “safe” account and dirty perv account.
Just like Reddit