Whey protein is used by athletes and body builders
because of the higher level of essentialamino acids, 
particularly the branched chain amino acids that are metabolized in the muscle not the liver. Protein is critical in repairing not only muscle, but many other body tissues. 
Whey is helpful for weight loss and building muscle in those who work out, but will do little to help build muscle in those with sedentary lifestyles.