Actually since its fullscreen windowed aka border less windowed neither resources (cpu) nor quality should be affected. Theres basically no difference between the two. The only way i can think of that i would change quality is if he was talking about windowed in which it wouldn't be full screen so it wouldn't really but full max res. For example with windowed mode in WoW using fraps the video on a 1080p monitor comes out as like 1800x900 or something so therefore when you play it back full screen there is a slight stretching. This is not the case with full screen windowed. In this case the only difference in the two modes is how windows handels the window thats all.
The resources used(cpu usage) might be different but in my past testing there was little to no difference.