Nothing but nothing has the accuracy (if needed) of the mouse.
I guess it a personal preference thing. The trackball was good for Cad because it was easy to spin 3-D models around. I use my trackball and mouse on my Linux machine now but I have my Mac next to my LazyBoy on an end table in the living room and I can just reach over to use the trackpad with little effort. lol It the perks of being retired.