One of the reasons I went through all the rigamarole of installing Neverwinter Nights — aside from a desire to play it again 😀 — was an offhand comment I saw on the Ubuntu forums a few days ago, about getting a slight bump in framerates in fullscreen games by turning off desktop effects.
I wanted to try it for myself, and to be honest yes, I got the same result. In NWN you can display a frame rate counter by entering ##trace fps in the Talk bar (but the counter doesn’t appear on screenshots, which means you’ll have to take my word for it 🙄 ).
But what I was seeing was a 4-6 frame-per-second increase (on average) when Appearance > Preferences > Visual Effects were set to “None,” and when they were set to “Normal.” Jacking up the visual effects to “Extra” didn’t seem to have any worse an effect than just “Normal.”
Again, I have no way of proving the slight bump, and I have almost no education on why or how these things work. But I do know enough to realize that there are a lot of factors at work here, not least of which is my relatively mediocre video subsystem. It could also depend on the game, or even just the graphic demands. And of course it’s possible that on a more powerful system that frame rate difference is negligible, or unnoticeable.
Be that as it may, if people ask (and sometimes they do), I’ll probably suggest they turn off their desktop effects if they plan on playing fullscreen games that require video acceleration. At least, it can’t do any harm. 😐
Motho ke motho ka botho 
It’s sound advice.
I am not an expert on graphics by any means, but it is logical. Visual effects of the Compiz variety (compositing effects) use the graphics card, even when they are not actively doing something fancy, because Compiz is still the one managing the screen with your game in it.
Metacity is likely not optimized for single screen, undecorated games either, but it relies on the CPU for rendering, not the GPU…
One of these days, I intend to sit down with a blank Xorg in Arch, before I put a WM on it, and try a game at full screen with frame rates counted. I bet it will have another small improvement. That’s how I use Hulu desktop and xbmc/boxee.