My Answer: In Volume One , I devote a chapter to 2 different types of bench press: the bodybuilding bench press and the powerlifting bench press. The powerlifting bench press requires that you squeeze your shoulder blades. This squeezing of the shoulder blades back stabilizes your body on the bench so that you can push more weight.
The powerlifting bench press, however, is not meant to build the chest. If you're looking to build the chest, then there is no requirement to squeeze the shoulder blades. It is simply safer to do so.