In sum, here are some points echoed by many people:
1. If color plays no importance for the strength of the image, it should be in black and white.
2. A black and white image typically portrays emotions better over a color one.
3. A stronger tonal contrast sets itself up well for a black and white image. It allows you to fill in the rest of the blanks with your mind.
4. Color should add a point of visual interest through the image, enhancing upon what is there.
5. If the colors cannot be saved, such as strong casts, the fallback is converting it to black and white.