In my experience supporting Mac users, it's about 50/50. I think a lot of them have been conditioned to not maximize windows because it hides everything else, and they don't understand how to get back to their other windows.
I don't maximize windows because it means a 1 second delay, as for some reason Mac OS still does the hardcoded workspace switching animation even for that. Which means entering/leaving fullscreen in a video player is also delayed every time. I don't get it, not even the accessibility settings can disable this waste of time.
