Another cool usage is to light up specific keys based on the current application. This is quite useful in things like games or editors. You can have green for movement, white for actions, etc.
I never got that one. Who is it for? When you're playing a game, you're not looking at the keyboard. And with just the few buttons available covered by your hands, it's not really for others... Why is the game-layout lighting a thing?
Its mostly aesthetics. It could be useful if you come back to a game after a break and you forget some of the keys. I can see its use as a training mode too.