Full screen or windowed mode for casual games?

one blitz game from yonks ago was window only at a small size at that (320*240 ish but perhaps more of a rectangle downwards) and on 1024 it was a pain to see what you were doing so you had to drop to 800*600 just to see the damn thing

so factoring in random monitor sizes and resolutions what looks great for you might be titchy for someone else
even if the casual gamers market still gets listed as using 800*600 their will always be others not