It's always a good idea to have more than one account in different servers in case one of them goes down, you get banned, etc. It's also a good idea to be in servers running different software. A software may stop being developed altogether (that's not Lemmy case, but has been known to happen) and been on servers running old software can be a security risk.
It would be great if nomadic identity were a possibility in ActivityPub, that will make things much easier, both in terms of posting and moving instances.