As in trackpoint, do you mean those sticks in the middle of the keyboard that serve as your mouse control? All I have to say to that is, "eww". Isn't that like SO 90's or something?
Anyways, one big reason that ppl use mouse pads for optical mice is that you have a sort of reflective surface or some weird wood grain or incompatible mousing surface that causes your optical mouse to not track properly. Another reason is to improve the "gliding" of the mouse and to reduce friction and resistance, I guess.