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.