Try to start thinking of light not only as a way of getting a proper exposure onto the film or digital sensor, but as a way of controlling your viewer’s emotions. When you start adding an emotional component to your photographs, you will immediately leap ahead of all the other local photographers.
Hard light is also good for defining texture and irregular surfaces.
Think of a bride in her wedding gown. Her dress is covered in lace and bead work.
How should you photograph her? Should you use hard or soft light?
If you position a hard light so that it is glancing across her body from the side, the shadows created will bring extra emphasis to the lace, stitching and beading.
If you feel the need to lighten the shadows, or lower the dynamic range contrast, you would just add a fill light. This way you still get the beads and lace to pop in your photos, but you also fill in and lighten some of the shadows.
Be careful not to use a fill light that is as strong as the key light. It will introduce competing shadows into your photograph.
What about wrinkles?
If your goal is to show an old weather beaten man with a timeworn, craggy face – the best lighting would be a hard light, positioned so that it is glancing across the face. The intense highlights and shadows would emphasize all the wrinkles and planes of the face.
Here is an example of the difference between hard light and soft light. Notice how the wrinkles are lighter and the subject appears younger with a soft light source!