Graduated compression stockings (GCS) help prevent the formation of blood clots in the legs by applying varying amounts of pressure to different pas of the leg. Thigh or waist-high stockings help reduce pooling of blood in the legs and help prevent lightheadedness or falling when you stand up (ohostatic hypotension). Stockings that rise to just below the knee help limit lower leg swelling due to fluid buildup Ref Davidson 23rd edition pg 450