I normally use the Apple Magic Keyboard and Magic Trackpad on my office computer, but when we leave town for a while, I turn them off so that their batteries don’t go dead and hook up a wired computer and trackball, and then I reverse the process when I come back.
This time, I left the trackball connected when I got home, since I had plenty of room for it. And I started using it in preference to the Magic Trackpad. It wasn’t a conscious decision to switch; I haven’t even done anything like photo editing where I might want the additional precision of the trackball.
Life is full of mysteries.