I have 3. Signed up to beehaw first because that's what people recommended on Reddit. After a couple of days realised I'd prefer a mainstream server and went to ml. And then .world launched and with the better hardware and admin I moved again.
So it was all logical at the time but it means the total numbers across all instances are misleading. I'd say many users have at least 2 accounts.
I've signed up to Lemmy.ml first, because it seemed like the main instance. My application was taking too long and I thought I messed up somewhere. So I signed up on beehaw.
Street that they defederated, I understand and respect this decision but I want to see all the instances so I created an account on Lemmy.world.
Then I discovered the solarpunk instance (slrpnk.net) and realized that this is a nice small community that I want to be part of so I joined them. Now I think I'm settled.
Some instances are faster than others due to server load. Not sure how well Lemmy.world runs or what spec the server hosting the instance is, but Lemmy.ml runs like a pile of dog shite compared to the smaller ones, it’s constantly timing out, with error 500s too. I had to make another account on feddit.uk instead as it runs much faster.
Also for example if lemmynsfw was completely defederated, if you wanted nsfw content from there, you would have to make an account there to access that content.
Fret not though, over time the opensource community will step in to improve all of this.
I made an account for memes and stuff. Then a more professional account. I'll probably make a porn account at some point, but not while the big porn instances are allowing loli and shit on their instance.