Guys, the problem and the advantage of a 120hz screen is that Optimus can't support greater than 60hz displays so a laptop with a 120hz display won't have Optimus and will wire the monitor / video outputs directly to the Nvidia GPU - removing the need to enable the Intel GPU - which will reduce CPU temps and remove a whole host of issues that Optimus brings.
Without Optimus, the discrete GPU will be downclocked to run on battery. With the new Maxwell generation(s) the battery draw will reduce over the previous Kepler GPU's, and as Nvidia increases support for battery saving features and further advances in process will continue to drop the battery requirements, removing the need for something like Optimus.
Hopefully Asus will make a higher refresh 1080p without Optimus someday