Unless you're doing something really artsy, color photography has to be fairly accurate. If colors are different you are likely going to feel that something is "wrong" with the photo. The sky may be a slightly different hue of blue, faces may have a weird tint because of the lighting, etc. There is an expectation of accuracy in color photography.

With black and white pictures you can pretty much do whatever you want. A cloudy sky can be changed to look light and soft, dark and with a lot of contrast and mood, or you can deal with bad lighting color by going monochrome. Either would look Ok and not give you a feeling of something being "wrong" with the picture.

You can play with contrast, exposure, or saturation (making things that were blue in the original image appear darker, or the green of the trees appear with more contrast in the black and white version). You can create your own interpretation of reality with monochrome images.