MapleStory isn't that heavy of a game that you need 100% focus on it. Playing it full screen is virtually pointless unless you have a 1024x768 or 800x600 monitor... And no one should have a monitor with that native resolution. I'm always moving out of MapleStory to check something else so playing in window makes it much more convenient. Also alt-tab always causes glitches and builds up RAM usage for some games.