The whole purpose of a photograph is to document a message, a moment, or at the very least a feeling. With black and white photographs this message or theme is more easily conveyed to the audience because there is less in the photo to dirstract you from it. Every photograph you will ever see will have colors, composition, at least 3 elements, and a theme that will make up that photograph. Unless of course it is a black and white photograph. By using black and white photographs instead of color the artist removes the distraction of color, causing the audience to unknowingly look at a specific element of the photograph. Doing this conveys the feeling more directly than if you were taking a color photograph. It is a very simple eye manipulation that can drastically change what you want your audience to see.
What does this portrait make you feel?