I usually photograph against plain backgrounds because that is what is available at studios. However, if I do it correctly, the images may be given a boost in post processing. By keeping the background uniform, it can (almost always) be replaced. A medium gray background is best, but even white or black can be changed. This gives a great opportunity to "finish the vision." It also gives me a chance to experiment with variations so that when I do have backgrounds, I will know which background will work with each shot.
I also use other techniques to "spice" up the images. These special effects include line drawings, frames, composites, grunge overlays, and so on. Sometimes a combination of techniques do the best job -- whatever helps to tell the story is fair game!