Possible spoilers...I don't know.

If you look at the map from the opposite side of the glass (so you're in the room with the EXIT door) and line up the reflections with the map it looks like it outlines places you haven't discovered yet.

http://steamcommunity.com/profiles/76561198041202241/screenshots/

It's not incredibly useful for solving puzzles but you could gauge your progress by it...maybe. It's a neat Easter egg regardless.

Wow, that's awesome! I didn't notice that.

It pretty amazing how small details like this can be missed from first playthrough.