That would be so useful, because most apps don't go near full screen size in mac. Garageband does, one of the very few. This would be most useful with browser windows because if you "maximize" a internet window (mac makes it as big as neccessary) and then you go to a page which is longer or wider, it doesn't resize it. IT forces you to manually drag the laggy corner to the bottom left corner of the screen. You would think that Apple would integrate automatic full screen in their next OS but they haven't.