I think he meant (or this is certainly what I was hoping for) that removing the optical bay would leave space for a much larger battery.
Ah, that makes more sense. Although a battery is a lot denser than an optical drive, so that would kick the system weight up. If you use some of the space gained to instead make the system thinner, you start to get essentially a Macbook Air. And I think it's fairly clear that Apple is moving in the direction of converging the Air and the 13" MBP.
I doubt the optical drive uses any significant power at all when it's not in use.
That said, I ditched my own in favor of an SSD + HDD setup and haven't looked back.