On a track you are riding faster and braking harder than on the road. The tyres heat up a lot more and as they heat the internal pressure rises. You start with lower cold pressure so you end up with the correct pressure at operating temp. Moto GP bikes start with a cold pressure of 22-24psi afaik.
Do not reduce your tyre pressures for potholed roads. All you will do is get wierd handling, possible rim damage and greatly reduced tyre life.