Some demos, back when the Demo Scene was more lively, used the keyboard leds as an added visual fascination device of some sort.
Music on your adlib card, moving shapes on your 320x200 256 color display, and some 80s Knight Rider style moving light effect on your 3x1, 2 color keyboard led display.
Humanity was once hopeless.
I don't think that's useful. Some people apparently did.