My wrists have "barely carpel tunnel" according to the one doctor I went to see. I find not having to move the mouse all day with my wrists (as well as a split keyboard with risers) has eliminated my wrist problems at work.

Easier on my wrist, less arm motion, and my hand doesn't lock into a claw shape after using it all day.

In the past my wrists used to hurt, my father had carpal tunnel and I didn't want to risk it, so I switched to a keyboard centric WM and switched to a trackball. I haven't experienced wrist pain in years, although I think it might be mostly related to the keyboard centric WM since I went back to a mouse for gaming a while back and when my trackball broke I didn't bother getting a new one.

That being said trackballs are amazing for working on limited spaces or soft surfaces (e.g. a couch or bed), once I've gotten used to it I could work on the sofa just as efficiently as I would on a desk without extra monitors, but now my desk has two large monitors and plenty of space for the mouse, so it's less of an issue.