This feature would be very usefull in connection with little displays. I work now with an industrial 9' 800x600 (as main stop control) and every pixel is precious. Full screen (ctrl+shift+win+alt + function key !!!) would mean that only the "organ" would occupy the screen, none of the windows bars, program menu or settings bar (the bar with SET <> etc).
Well I must say something about my setup, since this is cheap and good and makes clearer the Why. On the 9' display comes a membran keyboard. The base of this kb is thick acrylic board with thin copper wire glued on it, then comes a separator made of a simple plastic sheet (for old fashioned beamer) with holes for the contact plates and the top is also a platic sheet with stops names and colors printed on it and little tiffany copper ribbon as contact plates. All this is connected to a keyboard, only the controller remained, of course. Now, each key allows only one switch. Thats why one-switch-keys (without modifiers) are very welcomed.
(The GUI of the VPOs are modified to black (off, no light goes through the membrane) or white (on, the stop is lighten) and give a visual signal through the membran, to verify if the stop is off or on).