Currently I don't actually have any use for this function. In the past there have been several instances where one would need such a function. Take for instance, Steve's underwater module. Having the rippling effect of everything that is drawn to the screen. Then there's tons of modules that Monkey wrote that "fake" this requested function by drawing everything to the screen layer by layer sorting through by drawing order (where the caveat to his method was the obvious walkbehind issue).
Anyway, I just assumed it was something terribly easy to accomplish since AGS is already doing this - if not, then don't worry about it.
Of course, with this function, you would always be one frame behind the current frame.