Just to clarify, all the Lemmy servers you can join are interconnected as if they are just one big platform with the same content, so the experience is pretty much the same regardless of the server you join. The server you choose is just your door into the Lemmyverse.

Each server may have slightly different policies, but ultimately the goal is that you don’t have to think about it (other than knowing which server you are a part of so you can log in). However, it’s smart of you to consider how big a server is as some of the small servers might be more likely to shut down due to lack of maintainers or funding. That’s the main downside to the not-for-profit, decentralized nature of Lemmy/Fediverse—but so worth it in my opinion.