This article is about mastadon instead of lemmy, but that doesnt really matter: https://ianbetteridge.com/2023/06/21/meta-and-mastodon-whats-really-on-peoples-minds/

I especially like this bit:

Mastodon is not a social network, which is where I think John and Dare start from. It’s a set of communities which may, or may not, choose to connect to each other. Those relationships are based on shared values and trust: my instance connects to yours because I trust you to moderate effectively, not allow spam, or whatever other ground rules we can agree on. Some communities choose to apply this loosely, and some more strictly (some communities, for example, won’t federate with others who don’t have the same expectations around moderation for everyone they federate with).