It is true that bouncing the board multiple times in a row before take off (trampolining), causing substantial deflections over and over again in a short period of time, is an activity that could shorten the life of the board.  The board was not designed for that type of activity and may crack, break, and/or show other signs of damage as a result.

Most certified pool operators post notice that multiple bounces are not allowed because it is an activity that greatly increases risk of injury to divers of all ages and degrees of experience.