I'd say most pro players have everything set to low/very low.
Personally I always have textures/model set to high since it doesn't affect my FPS in the slightest and the game looks nicer.
Anisotropic Filtering to x16 which again makes the game look less blurry and no FPS impact.
I always have MSAA turned on, 2x on native res and 4x on lower than native. Doesn't impact FPS on my machine but gets rid of all those annoying jaggies.
Rest of the settings are on low because I'm heavily CPU bottlenecked thus Effects, Shadows and Shaders impact my FPS by a lot. If I had a good CPU I'd probably play with everything on High.
Having shaders+effects on High/VH makes it easier to see through the molotovs and having shadows on High/VH allows your to spot enemies' shadows from greater distances e.g. you can see people standing on top of cat all the way from mid on Dust2. Obviously shadows isn't something you'd utilize to this extent EVERY game but as I said, if I had good FPS I'd sacrifice some to get this kind of advantage.