Side on losing hazards
Spinning Balls into Open Pockets
A spinning cue ball entering an 'open pocket' has a greater chance of entering the pocket than a plain ball shot. The ball may bounce off the 'wrong' pocket jaw but will probably then hit the other jaw and spin in. So in general, any side will help the ball into the pocket.
Spinning Balls along the cushion
A spinning cue ball running parallel to the cushion, with cushion side on it has a much greater chance of entering the pocket than one without side. The same cue ball with the opposite side on has very little chance of entering the pocket.
Side WIDENS the Pocket
By using side, some losing hazards can be made much easier than if you played the shots plain ball; the pocket is effectively widened and the shot is made much easier. A good example of this is the thin in-off along the cushion. If a good player played this shot plain ball he/she would expect to get the shot around 3/10, but with side he/she would expect about a 9/10 success rate.