I pump to 5 psi over the rated max because bike tires seem to lose pressure over time and I will finish the day at max pressure, and not have to pump for several days. When I do pump, about once a week, the pressure has dropped a few pounds.
You will get the lowest rolling resistance at max pressure, and this tempts some to over pressurize the tires. Not only does this over stress the tire, it doesn't do as much good as they may think. The physics of it is that there are diminishing returns. Over pressurising the tires minimally decreases the rolling resistance. The more you over pressurise the smaller the gains in decreased rolling resistance get.