Sharing and remote streaming, plain and simple. I have no problem setting up accounts for friends, but choosing your server is a pain for some. But the bigger problem is that the first thing anyone will say is: Don’t expose Jellyfin to the Internet. That’s a bit of a problem.
And they’ll then say, “Oh it’s not so bad just set up wireguard and…” This is the ramblings of a lunatic. I’ve been working with tech a long time. Tech is my job. It is my hobby. I do all of it from repairing my own hardware to administering servers to running my own home lab to doing open source development. Wireguard is not friendly. It is not something I’m going to set up at every friend and family member’s house so I can share my library.
I’ve got a more secure but imperfect setup in sticking Jellyfin on the Internet behind a proxy that requires login. But this is not something most people are going to want to deal with. They want to stand up their server and then share it with people.
One thing is prioritizing security. There’s a number of known flaws, of varying severity, which is why most people would recommend not exposing Jellyfin to the Internet.
Perhaps they could set up a second project, a Jellyfin meta-library, whose whole goal is to be exposed to the Internet. You stand that up, give it access to other Jellyfin servers, and it handles the work similar to STUN of connecting you to media on those servers. This would make it so people could share easier.