We humans are plantigrades. That means our feet rest flat on the ground. We have large, bony heels to make sure that our flat feet stay supported under our vertical legs.
But among mammals is another popular method of support--digitigrade, meaning that the animal walks on its digits, or toes, and keeps the rest of its feet off the ground. Our closest picture of a digitigrade human is a ballerina:
The only problem is that even the most experienced ballerinas can't keep to the tips of their toes for long. But what if they could? The most obvious thing would be to reduce or eliminate the heel, as a large ball of bone would not be necessary if the majority of the foot is off the ground. What advantages would standing on tiptoe bring to the human species as opposed to putting the feet completely flat on the ground?