Processing a raw file often produces images which are over- or under-exposed in localized areas. Double or triple processing a raw allows you to target the tones in every area of your image for maximum dynamic range and tonal control. This is an example of a raw file processed once with a global curves adjustment to improve contrast. Note how the highlights are near blown and the shadows are near black. The raw file was then re-edited and blended in multiple times to target the tonal values in each area.