Earlier versions of OpenGL and graphics cards required all textures (images) to be a power of 2, eg, 256×256, 512×512, 1024×1024, 2048×2048, etc. Later versions support textures which aren’t a power of 2. For panoramic VR use, this means that the textures used to represent the panorama can very closely match the original media, for example, displaying a cube face size of 1392×1392 instead of of downscaling to 1024×1024 which would result in a slightly less sharp image. Generally, if your graphics card supports them you should use them to get this benefit and the option is on by default. Your graphics card supports non power of 2 textures if it supports Quartz Extreme, Mac OS X’s OpenGL accelerated display mode. If not, the checkbox in the Advanced Preferences will be dimmed.