I moved from Lemmy.ml because I liked the name of Lemmy.world and it ran a newer Lemmy version which meant I could make communities. I moved from Lemmy.world because they defederated from piracy communities they didn't even host (but for some reason still kept the small piracy community they DID host) From thelemmy.club because I couldn't see the Hackintosh community from there (probably defederated) Now I spent some time looking on join-lemmy.org and checked out some instances and this (lemy.lol) instance seemed good, so I chose that.
You're still dependent on a single point of failure, what I'm talking about is doing like any other website but instead of using a provider like AWS, you've got a bunch of people all over the world providing storage space and bandwidth and all data is stored on three servers in different locations at all times so there's basically no reason for the website to ever crash.
If you were to access Lemmy from a web browser you would need to remember what server you're signed up to because that's the website you would need to go to, you wouldn't be going to "Lemmy.com" or whatever.