Sometimes it may be just possible that you want to add a tone to an image which your camera did not capture or something that you cannot achieve with the lens. Photoshop can help you get that special look, especially for models.
Here is a free stock image.
The same image with the tone changed.
Here is another effect.
And, here is another. The possibilities are limitless. It is very easy to do. The tutorial is here
Other Photoshop tutorials are here