As far I'm aware as a casual user of Galaxy, you're correct. It's just a convenience application with some light social features.
I find it slightly more convenient when installing games on a new machine. I've never personally seen a game that required using it.
Yeah, I'm remembering the time immediately before Steam launched, getting a computer set up with games for a LAN party or whatever, someone sharing a folder of installers/updates from their HDD so everyone could be on the same version and whatnot. .. and that was the best-case scenario. Sometimes you just don't play a certain game because half the people have a different version or whatever haha
Convenience is 100% Steam’s most important feature. Finding games, installing them, updating, auto-login, cloud saves, probably more that I can’t think of right now.