A possibly better example for photos would be the 8 bit tag that says a pixel is within -2 to +1 in each of RGB. In 8 bit, there are a lot of cases where this is a big enough range to capture the noise of a static color (and or a gradient). In a 16 bit image, a lot of the time there might be 3-4 bits of noise which will mean that the tag is a lot less useful.