*Most pressure cookers have a working pressure setting of about one atmosphere (100 kPa or 15 psi gauge pressure), the standard determined by the United States Department of Agriculture in 1917. At this pressure boost relative to sea-level atmospheric pressure, water boils at 125 °C (257 °F).
The higher temperature causes the food to cook faster; cooking times can typically be reduced by about 70 percent. For example, shredded cabbage is cooked in one minute, fresh green beans in three minutes, small to medium-sized potatoes cook in about eight minutes (depending on thickness and type), and a whole chicken takes only twenty minutes. Brown rice and lentils and beans can be cooked in ten minutes instead of 45.*
I thought the pressure also caused the spices etc. to permeate the meat better.