Famous large format black and white photographer and darkroom magician, Ansel Adams once said:
"Dodging and burning are steps to take care of mistakes God made in establishing tonal relationships."
I've read all of his books on photography and the zone system. He knew his craft especially the materials of film, photography paper and chemicals in order to achieve his ultimate vision.
As Adams said "You don’t take a photograph, you make it."
When he was at the camera view finder he would visualize the final image in his head and then work accordingly, knowing the limits of his film, exposure and his abilities to dodge and burn in the darkroom. Digital photography is no different. The human eye can see an amazing tonal range that our cameras and sensors can not record. It is in the post processing that the artist can complete his final vision.
Ansel was also a musician and he saw the negative as a score in which various versions could be made. He kept notes on his development and darkroom practices for each of his masterpieces but could also revisit and image. He even left behind his negatives to the University of California so future artists could experiment with them. Here is an example from my own portfolio of an image re-imagined. Here is the first version of the hay bales on Prince Edward Island:
A straight-forward interpretation of the scene. The composition is nice but I wasn't satisfied with the sky and there wasn't any sense of drama. Farming is hard work and there is a bit of a gamble to cutting hay. You have to judge the weather because you need three days of sunny weather after the cut before you can bale. Farmers hope to get a couple of hay cuts a season and its all about having the weather cooperate. This second version brings forth a lot more drama to the sky:
Sometimes an image just has to sit and peculate in your mind for a while. The first image was developed right after our trip to Prince Edward Island. I was eager to create a slideshow for friends. The second version came four months later.