It's an easy way to get remote access to services when away from home, or when the family lives in different homes but wants to share services. I wrote a guide explaining how to set up remote access for Jellyfin using Tailscale[1], which may illustrate the use case.
[0]: https://tailscale.com/kb/1084/sharing/ [1]: https://www.ethanmad.com/post/jellyfin_remote_access/