It's also great for sharing files with friends/family. I gave a couple of friends a folder address, and we all just drop shit in there that we want the others to see.
Try it out. It's free. Install it on a PC or phone, set up a shared folder. Put something in it. Set up syncthing on another phone/computer and use the same folder name. The program takes care of all the network stuff.
And so many other things. I've also used it for "cloud saves" back/forth from my desktop to my steam deck on games that don't support them for various reasons. Dyson Sphere Program being one, because the files can get quite large.