I have heard countless times, you dont need to set your desktop or play your games above 16bit, you simply can not see them, or there is no actual visual improvment that is visible by the human eye.

It depends on what video card you have. If you have a 2MB S3 Virge DX or something like that, you might want to stick with 16 bit color because you might be waiting for a second or two for the screen ...