I won't vouch for the productivity savings from moving your hands less, since I think that's an absurd micro-optimization. Rather, I prefer it because I find it to be quick and accurate. After a week or so of getting used to it, when I first got a ThinkPad that only had it, it became the most natural and comfortable way of navigating. Not having to repeatedly paw at the bottom of the laptop and confort my hand to make a click (or deal with a single-finger click0 has been nice.

Mind you, I'm only speaking for the real ThinkPad trackpoints. The one in a Dell laptop I had for work was nowhere near as comfortable, and felt slippery and awkward.