I don't know anyone that does this type of thing to play on pub servers, but all players who play for decent teams try to achieve 125, 250, or 333fps. It is a known fact that it makes a huge difference to CoD games and how you move/shoot. Its not the same for other games but it is certainly that way with CoD.
Seems stupid tbh, I'd hare to be in decent teams playing at 800x600 all low, seems like everyone wasting there money on graphics cards.