Used a trackball since 1994. Desktop publishing and photo editing, if you've ever needed to position precisely and lift finger off the ball and click or mousedown without moving the focus again you'll just know.

Kensignton makes a good one with a scrollwheel ring around it, the ball XY is perfect though the clickers are so-so in longevity. Working without a physical middle click and two button software middle click emulation is frustrating sometimes.