Why do nurses roll over paralyzed people from back to stomach and back again?

When people lay in the same position for a long time they will get what is called Bed Sores. These come from constant contact with the sheets which will rub on the skin and not let air get to the skin. Rotating the patients position helps to avoid this. It's also for circulation reasons. Blood needs to flow to all parts of the body. When you are in the same position blood has a difficult time going where there is pressure applied from laying still. Rolling over helps circulation also. Plus it gives the patient a different view.