I am part of a network of "Plex admins", meaning each one of us own and maintain their own Plex server with their own library.

Thanks to the centralized Plex account, we can share our libraries with each other in a few clicks.

You can do the same if you don't have a server also, basically being a member of various Plex server and accessing everything through a single account and interface.

Sure, requiring an account if all you want to do is being the single user accessing your own instance is useless, and if it's your usecase, then Plex is not the right tool for you.

I tried Plex, Emby and Jellyfin, but I staid with Plex because of this easy sharing feature.