I don't mind losing eye candy for the sake of smoother running but what worries me is losing essential details. For example turning down 'Building Amount' can cause the computer to not bother drawing the target you are looking to drop a bomb on or can remove the hangars from the airfield you are trying to return to so you cant find it. Dropping the settings related to ground details loses you nothing when just flying around but it can mean that when you RTB the runway is invisible until you are almost over it.
On the other hand, the other day I tried turning down the resolution to solve an annoying tendency to go into slide show mode when diving into a large group of enemy aircraft and although the result was horrible 1980s style grainy graphics the ground targets stuck out like a sore thumb! I did not get a chance to see if it made enemy aircraft easy to see because the graphics were so horrible I changed the resolution back
If anyone knows what settings would help me see enemy aircraft I would love to know as that is my biggest problem playing COD