When you sleep on your side, your shoulders and hips stick out more than other parts of your body. Plush and Pillowtop mattresses have softer padding that absorbs your body's curves in order to spread out any potential pressure points. A pressure point is an area where pressure restricts your blood flow and triggers a sub-concious mechanisim in your brain that causes you to change positions in order to restore blood flow. If the padding is too firm, pressure points increase, and we end up tossing and turning throughout the night.