Cropping refers to the removal of outer parts of an image to improve framing or to accentuate subject matter. It can be used to de-clutter a picture and draw the eye to a certain area. It can also emphasize the portion of the subject matter which caused you to take the photograph in the first place. The image below is an example of that.
While photographing a small group of horses it was noticed that the stallion was very protective of his band. He was keeping a close watch on my every move and would put himself between me and the mares. He was big and intimidating. While processing these images, I found that by cropping the image, it highlighted these points.
By eliminating the surroundings, including parts of the horse itself, it encourages a person to focus on the forceful stare that is sending a clear message. Including a lot of his long mane emphasized his experience and wisdom. Cropping the image in this way also makes the scars more noticeable which in turn helps with promoting his intimidating nature. A shallower depth of field was also advantageous as it blurred the background, again directing the viewer to the detail in the horse's face. Cropping can be a very simple way to make an image more interesting and powerful.