In stock photography, "trick photography" or special effect photographs are very useful. They can evoke metaphors and when placed in a specific campaign they can take on meaning that a more straight forward photograph cannot. Plus the 'off' or strikingly otherworldly images pull in the viewer, pique curiosity and hold the attention of customers longer than a more simple image.
While it's possible to create special effects with Photoshop, it can be hard to make it look eal. Check out Evan Sharboneau's book on simple trick photography techniques, Trick Photography & Special Effects, to create more realistic looking special effects with your camera.