Actually unless you're skyboxing the backfaces and faces not within a map area get culled by BSP automatically, making it essentially useless to spend the time NODRAWing things.
The thing about models, too, is that unless they're really complex (and I mean really complex) then they don't put too much strain on the system. I can have loads of props in the area and unless we're trying to phys simulate them all they're not going to tax my crappy video card.
Dynamic lighting on the other hand ;x