Wolf pups will lick their elders' mouths as a begging for food, but it has also been seen that other pack members will mimic this "puppy" behavior with their alpha. It is believed that when the adults do this it is more a sign of greeting/homage to their alpha than a desire for food.

I think just as there are different barks, there are different "licks." With my own pups there is the rapid, excited licking of the face, and that reminds me of the puppyish greeting of their elders. Then sometimes one will settle and systematically lick my hand or foot all over, and this to me is more of a grooming behavior, the bonding with the pack as Tikeyas mom mentioned. Finally of course there is the "tasting" aspect, like the skin lotion, or I know when ever I put chapstick on Tasha tries to lick at my lips because she smells it. I'm not so sure on the "salt" theory. Certainly if they are licking you while you are sweating that would seem to explain it, but I think overall there are varying behavioral reasons and no one explanation that fits every case.