RAM on a graphics card is the memory devoted specifically to handling images and graphics output to your monitor. Complex graphics, like in sophisticated games and movies, require some graphics memory.
For high-tech games, the graphics card has to display a new screen continuously. The purpose of video RAM is to refresh the display as fast as is needed. A part of the graphics card’s memory that holds information before it is sent to the monitor is called the video buffer. The video buffer is also called a screen buffer or a regeneration buffer. Buffers that can hold more than one page, allow quicker display updates because one page is displayed while another is being loaded.
For complex scenes in Maya navigation becomes easier with more ram.