THERE ARE SOME occasions when a photo can be improved by converting it to black and white. Typically, I find these are photos taken at night, particularly with high ISO under sodium vapor lighting. Here is another example:
The shadow detail here is weak, and all my standard techniques for lightening dark detail looks unsatisfactory. But after converting the image to black and white, I was able to put severe curves on the image, as well as high levels of local contrast enhancement.
You can bring up large amounts of shadow detail in a monochrome image.