Traktor's cue points are a handy way for DJs to jump around and keep track of different events within a track. For example, the guys at DJ Tech Tools use cue points to highlight the first beat, the best start point, and vocal cues (as well as trigger points for sample loops).
Myself, I use cue points in a more traditional, yet universal manner. I've been using a technique I call the Countdown Method for about a year now. Basically, cues are used in reverse sequence (as in 3-2-1 go!) to coordinate mix-in and mix-out points.