The more you inflate a tire, the less rolling resistance you have. But the more you inflate a tire, the rougher the ride.

Further inflation past 100 psi, really will not reduce rolling resistance significantly.

Another point, is to be sure to put in enough pressure to keep the tire from deforming noticeable under your weight. Deformation can cause "pinch flats" which are a bad thing. A heavy rider on a really thin tire will need to put in more then 100 psi to avoid pinch flats. Of course, a heavy rider would be better off on a slightly larger tire. The larger the tire, the less pressure required to support the rider's weight adequately. If you want a slightly more comfy ride and you don't care about a bit more weight, go with a tire size one spot larger. Larger tires should also give you a bit more wear.