I’m not PC but, one benefit of using a central server for syncthing is an always on backup that doesn’t require another client device to be on, it also allows for easier creation of new shares.

For example, with syncthing you can set the “servers” client device to auto approve/accept and shares that are to trusted devices, then when you get a new device, instead of needing to add that device to every device you share on the syncthing network, you only need to add that device to the server and then you can have your other clients connect to the servers share instead of device to device. It’s easier. You can also configure the shares on the server to use encryption by default too, since you don’t really ever need to actually see the files on the server since it’s basically a install and forget style client.