A lower pressure would yield a larger contact patch. At the track, this is good. Also, at race pace, tires get much hotter, and the internal pressure difference between cold and hot temps. is greater. Thus, if you start with reccomended cold pressure, once you reach operating temperature of the tire, it could be WAY over-pressured, making you more prone to blowout. Also important is the converse thinking...that a lower tire pressure, ceteris paribus (all things being equal), allows more flex, and thus greature temperature, which is, to a certain extent, good for a race tire, it being designed to stick better at higher temps.