Intel showed off a demonstration of Microsoft's DirectX 12 at SIGGRAPH 2014 to illustrate the CPU power reductions made possible by this new API. The test was performed on a Microsoft Surface Pro 3 tablet with Intel HD 4400 graphics, the tablet ran a demo of an asteroid field with 50,000 unique asteroids in it, each with a unique combination of vertices, textures, and constants. The demo was programmed to allow switching from DX11 to DX12 with the press of a button.
To illustrate the power efficiency gains of DirectX 12, Intel locked the framerate of the demo and ran it in DirectX 11 and DirectX 12 with exactly the same content for an equal period of time. The overlay in the screenshot below shows the stark power reduction when switching from DirectX 11 to DirectX 12, the CPU power consumption basically halves!
The chip giant showed DirectX 12 can also achieve massive performance gains. When unlocking the framerate, the performance of the asteroids demo jumped from 19fps to 33fps when switching to DirectX 12. In this scenario the power consumption remained the same.
It's unclear if this is just a cherry picked demo or a good representation of real-world workloads but it seems DirectX 12 is definitely something to be excited about if.
The power savings are coming directly from the efficiency improvements that inherently come with using the DirectX 12 API. Lower level access to the hardware than ever before allows applications to significantly improve their CPU utilization, enabling them to draw extremely complex scenes at a significantly reduced energy cost.
Like the Surface Pro 3, all devices which support DirectX 12 can benefit from DirectX 12 reduced power consumption, either in the form of longer battery life, increased performance, or some combination of the two.