Remember x11 was initially a client server model, where multiple clients could access a single x11 server. This brought a lot of complexity we don’t use these days
Starting a GUI app on any machine on the network and have its windows display on my local screen is vital functionality.
It's worth noting that the "client" and "server" are flipped from what was typical: your screen on your desk is the server and the client is a program running on some expensive machine on a rack somewhere.
It's still really cool to be able to spin up a GUI app on a remote machine, and use it like it's running locally.