I started to use a trackball (Kensington Orbit, because of the scroll wheels) when I began to notice that my hand hurts when using a normal mouse. I wasn’t a big fan of the rodent to begin with, and preferred to do as many things with the keyboard as possible. This is partly because I’m a tad clumsy, and operating a mouse was often annoying. My coordination with it was abysmal, and I hated to wiggle it around on my desk. Especially when I had to cross large areas, which involved picking it up and placing it further away, just so I can pull it down again.
With a trackball, I have much more space on my desk, since I don’t have two wiggle a mouse around. My hands feel better, and surprisingly, I’m much more precise with it too! It appears that while my hand coordination is awful, my fingers are fine.
Took me a few days to get used to the Orbit, but I have been using it exclusively since then, even for gaming (unless I play with a controller).
An interesting tidbit, is that back in the early 2000s, I helped a friend of mine run a computer lab, and they had Logitech Marbles there. I hated them, with a passion. I was reluctant to try a trackball, because of this. But somewhere along the years, whatever made me dislike trackballs, vanished. Now I love them.
Mind you, I’m not entirely happy with my Orbit, and will, eventually build my own. It’s going to be a long process…