Just joined Lemmy today. From what I understand, there are different Lemmy instances that host different communities. I supposed that to interact in a community hosted in a certain instance, I would need to create an account for that instance. Ended up creating 10 different accounts.
We don't have a good sense of which instances are going to be durable long-term yet.
Additionally, If you only have one instamce, you're signing up for that server's bespoke curation of the Lemmyverse.
I currently have (I think) 5 accounts spread across Lemmy and Kbin for these reasons.