Here's a good use:
Secretly install afterburner on your friends computer, challenge him to a FPS Death Match, and then underclock his system right in the middle of your game.
Or better yet, get your wife addicted to World of Warcraft and then underclock the computer right in the middle of her Raid. Then use that to convince her to let you buy a new computer so it doesn't do that to her again. Instant new computer shopping spree!