Allows you to check your feeds from multiple devices. For example I usually read from my phone, but sometimes would like to check my feeds from my desktop.

You could just subscribe to the same feeds from multiple devices/apps, but then you have to manually keep track of what's already been read and that will quickly get out of hand.

Synced read state.

If I read from my mobile using NetNewsWire and then go on my laptop and read with the FreshRSS web client, I don't need to wade through a bunch of articles I already read.

Runs 24/7. Also, I already host other things on the server, so there is no added cost.