Most games let you change keybindings in games. Thats...a standard thing? I dont really use controllers on steam so..
Even still it is a nice feature to have because not all games would let you change controller configurations by default.
I am playing Darksiders 3 and far as I've seen I can't seem to rebind
controller buttons. With Steam Controller Config. I could reassign the attack buttons to say the shoulder buttons. I could even make it so by pressing say the L1 button on my DS4 when playing a game
it'll be as if I pressed L1+R1. So using Steam controller config you can assign 2 buttons that a game recognizes onto 1 single button on your controller.
To give a more easy example: The Street Fighter Collection does not have an option to Have 3 Punches or 3 Kicks assigned to L1 and L2, with Steam Controller config I can do just that. I am unware if they patched it in as after I assigned it using Steam Controller options, I didn't fiddle with the ingame controller options.
I also bought Star Wars Ep. 1 Racer, which didn't recognize my DS4 controller by default, with a little fiddling I'd just add the game to Steam Client, and re-assign buttons to my preference.
Video games didn't exist starting from the PS360 era, and there are older games that don't have native controller support, or were only designed to be played with keyboard on PCs. Steam Controller Configurations makes it more comfortable to play some games if one prefers to play with an X1, DS4, or even a Nintendo controller.
Just because it is a feature you don't use doesn't make it 'excess fat', because, at least, there will be others who use those features to their personal benefit. I don't use all the features on my PS4 such as Share factory and Play share, but I wouldn't call them excess fat just because I don't use them.
Heck here's one more example:
Thanks to Steam Controller Config, I was able to assign
mouse movement to my Right analog stick for playing Xanadu Next, as the base controller configurations in the game didn't work properly for me, so I wasn't able to access my inventory conveniently.