Moving into specific changes made to DirectX 11.1, Microsoft has made it much better at redrawing portions of the screen, such as on YouTube, where only the video segment should be constantly re-rendered. By reducing redundant redrawing of text and other static elements, there is less memory and processor cycle wastage.

via Windows 8 graphics: Microsoft has hardware accelerated all the things | ExtremeTech.

In all cases, faster and more efficient rendering will result in less hardware resources being used, and thus lower power consumption. In the entire cycle of Windows 8, improved efficiency and battery life are probably the strongest and most recurring themes. If the unremovable Metro Start Screen and Surface tablets wasn’t proof enough, this laser-tight focus on efficiency makes it patently clear that Microsoft’s primary concern is being competitive against Google and Apple in the mobile computing sector.