Some functionality that keeps me using the Steam Controller has been touchpads for movement, quick gadget swapping with touchpads, quick 180s/gyro activation with touchpads.
I use it to play games like Doom Eternal, Left 4 Dead 2, Spin Rhythm XD, The Finals, etc.
Sadly I don’t find myself doing the same on the Steam Deck opting for the joysticks instead, since I don’t find the placement, smaller size, square versus circle, and flat surface versus concave offering the type of consistency that I use the touchpads for on the Steam Controller. It feels more a touchpad appropriate for slow paced games or just desktop navigation than optimal for the way I use the touchpads on the Steam Controller. And I don’t see Valve delivering on the touchpad end that I would like with the next Steam Controller with all the inputs it would be fitting in.
One of the things noticed when trying to set up an edge to edge swipe output a 180 was how inconsistent it turned out to be unless I changed the rotational angle to be corner to corner. Which is even less ergonomic than swiping naturally. Smaller surface area probably made the 180 less consistent too with how much further the camera moves with small movements.