One of the first things any photography student learns is the important of having a broad tonal range in a photograph. A photograph that is either too "bright" or too "dark" is, theoretically speaking, not aesthetically pleasing. Fortunately, in photography, rules are meant to be broken. Sometimes having a vastly underexposed image can hide certain details not essential to the main thought in a photograph, or add an air of mystery to an otherwise ordinary scene. Most important of all, composing a shot with the intention of underexposing the final image creates a photo that's out of the ordinary. In the photograph above, taken inside the run-down once-popular Saltair resort in Utah, the main visual element in the composition is the highlights across the handrailing. The staircase itself is merely an afterthought, and thus does not need to be emphasized to such a degree.
Another important reason to underexpose an image is to capture interesting or visually stunning light. The art of photography itself is the capturing of light, and a good photographer holds the ability to recognize worthwhile light in a scene. The photograph above was taken on the freeway near Pleasant Grove, Utah. For most, the dance between the mountains and the clouds wouldn't seem special in any way. But at the time, I recognized that underlying layer of light that, in its present form, was simply too bright to allow for its subtle intricacies to make themselves known. Lowering the exposure on the photograph and increasing the contrast reveled what I saw in the moment which, for me, is the best possible outcome one can achieve in the post-production stage.