Nash Equilibria

Within Game Theory, Nash equilibria are used, somehow, to compute balance between players in a game.

The point of this post is to ask the question: WHY would you want to compute this?

I can only guess that if you're building a computer chess game, you want to make sure the computer opponent is somehow an equal opponent, not too hard or not too easy, otherwise the game would not be enjoyable.

But I fail to see how Nash equilibria would be useful for my work. I think this is because I haven't finished mapping the various components of game theory to my domain.