That doesn't solve the real estate problem - in fact it makes it worse in some apps. The top bar is still there after you do that. It just moves the menu items back into the window.

I don't really care where the menu items are. If the top bar would auto-hide, I'd be fine with it. I just don't want to give up the space.

Apparently there's a modified Unity called "Unity Revamped" which adds autohide as an option to CCSM, but it's a slightly older version of Unity, and for whatever reason I can't downgrade to it.