Back in the day, before shooting, photographers had to make a creative choice: shoot on color or black-and-white film. Now, however, you don't have to make that decision until after you've taken the picture.
This after-the-fact choice, thanks to the "desaturate" control on your image-editing software (or the ability to capture color and B&W in camera simultaneously), gives the creative process a new dimension, especially if the photo looks equally good either way. Take the following example:
I shot this crew member as he prepared the Staten Island Ferry for docking in the Manhattan terminal. The light hit at an angle that gave the image a dramatic feel. While the color scheme is unusual and interesting, I wonder if the color distracts the viewer from the drama of the light, or if it adds something to the image.I converted the photo to black-and-white, and optimized it to emphasize angles and tones. Which would you choose?
There is no correct answer here, but it is an interesting problem; the lesson is to always consider if removing color might add to your image.