Subtle, Shade, and SOS add a light and bright feel to your photos without changing the feel. So, if you are a color purest, or don't want your photos to be dated with a certain "feel" this set will simply brighten your photos up back to where your eye pictured the shot and not how your camera managed to capture the light.
SOS: The brightest - meant for a very dark photo in need of much light.
Shade: Works best on low lit photos with heavily shaded subject areas.
Subtle: Gives a slight lift to the brightness without changing the color.