Sometimes I use Photoshop to alter my final artwork so I can see different possible versions of the same image.
By seeing different outcomes, I am able to learn more about what makes a pleasing final image to me and incorporate those lessons into the next image I create.
A super-high-contrasty version:
A darker version with slightly more contrast:
While I feel I learned what I needed to learn about creating volumes and space using simple gradients, it is only after playing with the image in Photoshop that I feel I know what it takes to create a more pleasing composition.
Here's a look at the final Photoshop Enhanced Image: