Gamepads are used with the mouse, atleast all the ones I have owned and seen. Gamepad in left mouse in right. It's a miniture keyboard programable how you like. The one I have has 10 keyboard keys with 3 flipable banks + directional D-pad, and a volume or throttle wheel... all these are programable as far as what you want each i/o to represent.
I don't think the OP was asking about using a gamepad to control look direction...
I use mouse look a lot, but I never have it toggled on... I use directional (wasd) keys in left and hold left mouse button for mouse look. I too frequently need to move things around click extra stuff on bars to worry about toggling it on and off with my left hand, easy to do it with left mouse button.. All the game pad does is give a comfort feel and programablility to the left hands use.