Yeah, it's that exactly. For (FPS) gaming you want that distance to be as low as possible because you'll be lifting the mouse off the pad a lot and you don't want the cross-hair moving when you do that. Outside of FPSes it doesn't really matter.
For pads just go for something that tracks well and you're comfortable with. I prefer the very hard plastic ones purely because they stand up better to the punishment I seem to give things when I use them (YJ). I wouldn't go for the really expensive ones, I think they're mainly gimmicks. I wouldn't bother with one at all but the surface of my desk and optical mice just don't get along. I have one of
these and it's fine. No better/worse than other hard plastic ones I've had (both more and less expensive), I think they're much of a muchness really (got it cos it's big enough and not too expensive).