I can actually see a lot of uses for it. I personally think I would prefer it to a touchscreen.
One idea is to have it substitute in the place of the traditional right analog with the added benefit of precision. For example, you could navigate in a shooter with the left analog whilst controlling the camera with the touchpad. When you wanted to shoot you wouldn't have to move your hand just press the pad. Alternate fires and switching weapons could also be mapped to different actions on the pad. This may finally actually make shooters comparable to playing with a mouse and keyboard (if not better).
Navigating menus and inventory in/out of games.
Writing personal messages or typing via an on-screen keyboard.
Anything where a quick touch in the general vicinity would be more efficient than searching for a precise key. QTE's for example could make use of performing some action/s on the touchpad so that you aren't required to dance all around the controller.
Pretty much anything you could do with a full touchscreen or a mouse for. You would adjust fairly quick to the lack of a screen if a pointer was provided on the main screen to provide a relevant location.
How do you breathe again?
