It's not a feature. You can't just turn it off if more battery life is what you're seeking. The best you can do is increase the resolution to get more usable working space.
SetResX - looks like a shifty site but the application's golden. Lets you run a rMBP at 2880x1800 along with a good number of non-Retina resolutions by disabling scaling.
While I don't often use resolutions other than 2880x1800, which is what I use most, I find that animations seem smoother and battery life increases slightly when the Retina scaling is disabled. Nothing hugely dramatic, though.