Depends a lot on the tire and how you're riding.
+1 Depends depends...
What tire, race slick, street, dirt, bike weight, etc.
Race/trackday tires are built differently/special to run at unusual/lower tire pressures in order to generate more heat. Unlike street tires, race tires are engineered to need, embrace and leverage this extra heat. Reduced tire lifespan included.
Race/trackday tires on the street run at normal street pressures, they don't generate enough heat to operate properly. Race/trackday tires on the street with low tire pressures for heat generation and you risk dented wheels from potholes.
Sport and sport-touring street tires are engineered for the streets and to offer optimal grip over wider range of cold/warm/hot temperatures and conditions. Street tires are engineered to operate at normal street pressures, not trackday pressures. Run the pressure too low and they can generate too much heat, get greasy, potholes dent the wheels and wear out prematurely.
Tire pressures?
For track tires these numbers can be very specific to the tire/construction.
For street tires I usually recommend tire pressures based on the gross weight of the bike, sliding scale, x-heavy bikes 38-42psi. Middle weight bikes 32-37psi. Light weight bikes 24-29psi.
Dirt pressures are typically in the 14-19psi range, depending on the weight of the bike.
