Planning in advance is one of the mainstays for professional photographers. Be it the best time of day to shoot outside or making sure all the correct props are on set at the time of the shoot.
Photoshop is one of the tools a photographer uses to make the final project exactly what they are envisioning before the start of the shoot.
As an example, I had an interior shot to create where I needed to show the depth of the room and an example of how it could be set up. Fruit and pastries were brought in and the room was set up just how the client wanted it. I had no control over the time of day the photograph was to be taken so I had to work around that as well.
That was the first problem to deal with, time of day. Since the shot was in the middle of the day, I couldn't balance the interior light with what was seen through the window in back. So in the first set up, I shot an image to expose well for the outside scene through the window and then added one light to the table of goodies. I was shooting with a wide angle lens to show off the depth of the room so I didn't have a lot of freedom to place lights, or they would likely be seen in the final photograph.
As a professional photographer, I use Photoshop just about every day and the days I'm not using it, I'm thinking about using it. In this case I knew if I shot several images while the camera was locked down on a tripod, I use Photoshop to cut in the portions of the image that I needed.
Using layer masks in Photoshop, I was able to add layers of new photographs on top of the first one to make up the final image. Layer masks gave me the ability to show off portions of each new layer that would "light up" an area of the photograph.
So as I shot the scene, I would move lights around to light up certain areas. Then in Photoshop, I aligned them all up and created layer masks on each one to reveal what I wanted.
The final image has the lighting I was looking to achieve.
If you are looking to learn how to use Photoshop I am teaching Photoshop Classes in a small "hands-on" environment in my Pleasanton studio. Check out my classes here.