I made an account on another couple just for the heck of it. Some have different interfaces, or are federated with other servers that this one might not be. Also it’s like a backup - this one could disappear, be down for a couple of days, or decide that only AI photos of lemmings are allowed. Who knows. But yes, it’s not really necessary due to the way Lemmy works.

If you go to the homepage and select All, and perhaps Hot or New, then look at the top line of the posts that show up, you can see the different servers they were posted on originally. Theoretically voting and commenting on those works the same as communities formed on this server. You can see a feed of only communities on here by selecting Local.

One thing I noticed is subscribing to communities on other instances doesn’t seem to work - days later it still says “Pending” and I don’t know if that’s a policy or a technical problem.