Yeh I know they do it, just seems like cheating to me... if you wanna be "pro" shouldn't it be played on full like the dev intended?
Surely it makes you less skilled by turning everything off and playing it Doom 1.
Surely there is more to being "pro" than aiming and killing, things like cover, and being blinded by the sun etc should come into being "pro"... i.e. you find the best position to make kills and use dark/bright areas of the map to your advantage, which you can't do when people turn all HDR, shadows off etc etc.
Maybe I am too spoilt by Arma 2...