Graphic RAM (GRAM) replaces the constant communications between the display panel and the GPU when the screen is static by adding a memory cache, which displays the same image over and over and over again. When both the CPU and GPU both realize that nothing is changing, a screen capture is made and displayed. This allows parts of the SoC to shutdown, saving battery life and energy.
This is all happening incredibly fast, as you can imagine. The bottom line is a 10% increase in battery life. There are sure to be times when you will be grateful for every extra second of usage you have thanks to GRAM, before your phone shuts down.