I tried a little layering yesterday. More or less the first time I've used layering on photos this way. I usually don't do such extensive amounts of editing but am finding interest in the amount of colours this can bring out.
It basically involves splitting the photo up in several parts to bring out as much colour as possible. Regular retouching involves overall enhancing the photo whether in colour channels or just by shadow and highlights.
It's true that layer masks (PS) allow much of the same, but layering allows far more freedom.
Take for example the photo above. I split the photo up in three parts as essentially those are the three main colour and light divisions; the sky, the trees, and the water.
This allowed me to bring out colour and clouds in the skies, saturate and create greater contrast in the trees, and bring out a clearer reflection on the water surface without affecting each other element in the photo.
The photo is five months old and found just for testing purposes. It's not a very impressive photo and the edit isn't much to brag about either. Still, despite having done similar things before, it becomes quite interesting when applied to sky-ground photos.