The tldr to my understanding is it’s a bunch of different instances of the same thing (but not necessarily the same thing) which all have the ability to communicate, share data and allow users to interact across instances. This is why sometimes you see an @serverxyz after a username. It means their home Lemmy is another instance which is federated with yours.

So as an example let’s say I decide I want to run my own Lemmy server. I can impose my own rules, language of choice, admins, I could sell adds, ban a type of content etc. I can choose which other instances I want to be friendly with or cut off and they can choose the same for me.

Maybe there is a problematic Lemmy or one that is set up to house hate speech. I could decide not to federate with that instance cutting them off from myself.

So I guess why is this good… a few reasons that I’ve only come to learn recently. First off if you don’t like an instance you go elsewhere that better aligns with your values or interests or has a certain community you want to be a direct part of. Maybe you speak a different language and want to join one that is primarily in your language of choice or any other number of wants.

This type of set up allows for that where as something corporately owned and ran by a single company you get what they give.

That’s not to say every Lemmy is ran by some benevolent admin who doesn’t have some ulterior motives. But I’d you find this is the case there is little reason to stay and tough it out.

That’s my understanding so far. I’m new here and learning more about this every day. Take it all with a grain of salt