Your question has been answered already but to elaborate, if your interested. As long as your running OEM sized/ load rating tires (or close to it) you will want to stay with the recommended pressure on the door (or close to it) as that should provide optimal tire wear and gas mileage. If you were to make a drastic size change that pressure would no long apply, but you never want to use the Maximum pressure, unless you are at the maximum load for the tire in question. Which you would also probably want to avoid.
Lower Tire pressure, within reason, can give you better traction. Obviously there is a limit though, Probably a few PSI. If the pressure is to low it can cause the tires to over heat and fail, as well as uneven tire wear. The outsides would wear out faster becuase the center is not firmly on the ground.
Higher pressures will decrease rolling resistance and can actually help gas mileage (allot of OEMs spec their pressure a little high these days for that reason) but at the cost of traction. If the pressure is to high less of the tire is contacting the road which makes it roll more easily but since only the center is in contact you have less traction and obviously uneven tire wear.
As mentioned the tire pressure will also affect the ride characteristics of the car since the pressure in the tire determines it's stiffness and in turn how much impact it absorbs. I do not recommend adjsuting tire pressure to compensate for ride quality, that's what the suspension is for, but it does make a noticable difference.
If you're not sure what your tire pressure should be, or curious if you really have it just right an easy way to determine what it should be is to draw a line across the tread with chalk. Drive a short distance until the chalk starts to wear off and see if it's even. Again if just the center wears off your pressure is a little high try letting a pound out, or vise-verse. It's easiest to knowingly overfill them a bit for this test so you can just let the air out until you get where you want to be rather then trying to fill them in tiny increments.
If you really want to get crazy/ exact you can use an infrared thermometer and adjust the pressure until the tires temperature is consistent across the tread surface.
To much information yet?
