It is the type of attack that sacrifices power for speed. You are striking so fast and without preparation(suddenly from unusual angles) that you can only nick the opponent.Sounds like a good trick, but if you can cut his head, why not split his skull?
(Kind a like the difference between flicker and smash in boxing, one is used in a series of quick jabs, the other winding up to deliver a guard piercing blow)
Or taken from another angle an overhead two hand downward slash(like chopping wood with an axe) or 180 degrees wind up with a step in cut are very powerful but slow giving time for the opponent to strike first, or just side step.