Well, here is a bad explanation from Clive Cottingham:
There is no way the cue ball is coming straight back with only that much elevation. The Coriolis method of aiming massé quickly tells you that the elevation must be about 60 degrees before the cue ball can even go out and stop.
In general a piqué shot (to use the French spelling) is used to increase the amount of backspin in relation to the forward speed of the ball. It is used very often at the "small games" of carom billiards when the speed of ball #2 (the first object ball) needs to be reduced relative to the draw distance of the cue ball.