Bring out the full potential in a good picture before printing it or putting it up online. Even a proffessional photographer treats a shot, all images require treatment.
Inject the life back into people that has been drained by the digital camera. It's not photo "addition" but rather photo "correction." The camera drains color and life hue from people. Image treatment is meant to re-place the lost elements.
Its not always a lot of actual "change", but the slight amount, in the right areas, makes all the difference.