What's so special about the steam controller?

I use an xbox one controller for steam. Is the steam controller better if you play with the controller?

I also have some games in my Steam library. Some of them also support controller control, for example, I play the Farming Simulator with my Xbox Controller.

For me, it's not clear why you should buy a Steam Controller.

With the Steam Controller you can simulate mouse and keyboard. You do not have sticks, but touchpads. I like the Xbox One controller but more.