For 9/10bit, it means we don't have to upscale to 16bit before actual scaling or pixel format conversion, and thus a performance gain.
This means that precision is retained when scaling between sample formats with >8 bits per component (48bit RGB, 16bit grayscale, 9/10/16bit YUV).
Signed-off-by: Mans Rullgard <mans@mansr.com>