It absorbs light which prevents other plants fro being able to access it lower in the canopy. The absorbed light doesn't get converted to food, but is absorbed as heat energy which is radiated away.

To use your analogy, there is a set number of pairs of shoes available. Two athletes are to compete against one another. If one athlete wears one pair and takes all the others and throws them away, the other athlete has to run without shoes and will probably lose.