I just wanted to mention that too small instances can also be a problem: They're often not maintained very well. I experienced that the German community on "feddit dot de" was abandoned and I was annoyed about it, so that I was searching for a stable instance. Therefore, I switched to lemmy.world but now I think: meanwhile the German community is stable at feddit.org.
But I don't know why I now should move away from lemmy.world. I think the user base has to grow a little bit more. For me there is not really that much content in German, if so, then I would consider changing.
There is no need to change anything. You might consider making an account on another instance to be able to switch over if something bad happens with lemmy.world, you just start disliking it, or similar. But no need to change what works for you.
That's why I also only said that new users can simply be directed somewhere else.
Pretty much what the other person said. There isn't really a difference which server you're on, lemmy.world is fine. But we go on Lemmy because we want a robust network that isn't prone to central failure like reddit is - if theoretically everyone were on lemmy.world, then the situation really is no different than reddit. Someone could just buy the server/admins and do whatever they want, or the lemmy.world admins could just be evil in the first place.
For you not to be on lemmy.world is no disadvantage, just make sure whatever server you go to isn't a walled garden and stopped talking to ("defederated") lemmy.world, currently the only larger one that does that is beehaw.org.
Unfortunately (talking about federated services in general) there is a small bit of complexity that comes with spreading around the service across multiple servers. Lemmy tries to hide as much of it as possible from the end user, but it's impossible to hide the effects completely. It's kinda like democracy - it only really works well if every voter is informed, but even if they aren't, it's still better than an autocracy.
Not OP but I think they just meant it's pretty overloaded - it's one of the most well-known instances. "Too many" users can cause problems for the people hosting the instance, so I think there's been a movement to spread it around so all the eggs aren't in the same basket.