It's just preference based on how far back your monitor is on your desk versus how big your monitor is.
There is a bit of leeway for preference of relative size though, a bit like how people argue about it being better to move your mouse with your arm or your wrist. Some people like to look at everything and give their eyes a full range of motion - which I prefer to do, even though my screen is flat and my focal length changes from the edge to the center as well as the viewing angle. Factors such as viewing angle, focal length and perceived refresh rate can be off-putting to some people and as such they prefer to use windowed.
But at the end of it all, it depends on how well you can focus on successive hit circles... so the relative difference between players will not be that huge as it is mostly a factor of your viewing distance from the screen and how big it is actually (1920x1080 could be anything from 21 to 27 inches, but mostly 24). A lot of people still have smaller monitors.
