Although bounce was originally invented by Gene Sarazen to help players get out of the bunker better, bounce has become something that can be utilized out of the fairway and the rough as well. To get the ball to come off the club face in a predictable way getting the proper turf interaction is vital.
When a golf club does not have enough bounce for the attack angle of a particular wedge shot then the club will dig into the ground causing the ball to ride up the face and actually come off with less spin. To create that useful low spinning wedge shot the attack angle of the club head must be very shallow or there must be a lot of bounce present to shallow the club out quickly through impact. Therefore the amount of bounce that someone requires on his/her wedges will be based on the angle of attack.
Bounce is also useful because it creates a more forgiving interaction with the turf. If the club head strikes the ground a half inch before the ball and there is no bounce present then the ball will not go very far as the shot is chilly dipped. However, if there is sufficient bounce present then club will glide along the turf and then hit the ball resulting in a much better shot.