They don't. Pressure has to be taken off of the affected partl.
Pressure relief. Pressure ulcers need relief of the pressure as the primary treatment. A moist wound environment, treatment of infection, removal of dead tissue and treatment of poor nutrition/ diabetes/ poor circulation (pad) are also very important. Elevation of a leg pressure ulcer would be to relieve pressure or if there is swelling. It depends on the location of the wound.
Pressure relief. The first thing to do to a pressure ulcer is to get the pressure off. How best to do that? Elevate it.
Pressure ulcers. Pressure ulcers do not need to be elevated. You were probably told to keep your heels elevated off of the bed because we do not want your heels touching the bed creating additional pressure and injury.