The idea is to give depth perception. The problem with 3D is that when it was first made, companies for some reason thought it was a loving GREAT idea for characters to turn to the camera and demonstrate it to the audience. Sure it was cool the first time, but got really loving old really fast.
Anyways the main reason that I'm psyched about this is that Gmod will be 1000x easier with the ability of depth perception. Instead of gauging size of objects based on memory and flying around them, you'll simply be able to tell from just 1 angle.