Status indicators and other informational screen widgets get placed on a bar (or cross) across the center of the display. Instead of obscuring the window underneath, the compositing window manager maps the pixels around the bar. It's a bit disorienting to have a gap, but the user will get used to it. Possibly have an overlap region which is drawn twice on either side of the bar. Possibly the mouse cursor jumps over the bar.
This frees the edges of the screen for Fitt's Law things which are meant to be clicked often.