B&W photography captures just the light (to be more accurate the Luminescence), color can sometimes detract from what is important in an image, a bright red will draw the eye sometimes from what is important to the image, not every subject is good for B&W, other images it's suits perfectly. In short it handles contrast better, especially extreme contrast, bright midday Sun for example. On the other hand B&W can also capture the subtleties better, smoke and beams of sunlight through a window for instance.
