In terms of dark vs. light, and contrast, there are 3 basic ways to approach lighting a model: High key, low key, or normal key.
Normal key means you're going to light and expose and process the photo to contrast values that most closely resemble "normal." In other words, you're not going to use light and contrast, in very noticeable ways, to create mood.
High key images are bright with reduced contrast. Generally, they're used to create an upbeat mood. Conversely, low key images are dark with high contrast. The mood they create is more, well, more dark, emotionally dark, with much drama and mystery.
Art nude photographers often use low key lighting techniques to create drama and to increase the perceived artistic value of their photos. Many photographers, it seems, are quite "art conscious" since many in the traditional art world still hesitate to recognize photography as true "art." Personally, I don't give a crap as long as the check clears. Anyway, add shooting and/or processing in monochrome and low key images literally scream "Art!" to many people.
Using low key lighting, viewers are emotionally drawn to the mysteries the shadows represent. Regardless, those same art nude photographers can also use high key techniques and produce exceptional and very interesting work. With high key lighting, viewers are often drawn to the light, like moths to the flame. As such, high key can equally depict a perceived sense of art in photos.
High key lighting often requires more light sources than low key lighting. After all, if you're going to move much of the "light" values to the right on the histogram, it's going to take some light to do so. When shooting against a white seamless, for instance, it's often necessary to light the seamless separately from the model in order to keep the seamless white in the resulting captures. High key lighting also does a nice job of hiding imperfections on the model's skin.
Low key photography can be accomplished with a minimal of lighting. Often, but not always, a single source is used. Skin imperfections, of course, can also be played-down with low key lighting assuming you keep many of those imperfections hidden in the shadows. In fact, there are many things that can be hidden in the shadows yet still heighten the viewers' interests in the image.
Generally, high or low key images are products of a combination o production lighting and post-processing. From a post-processing perspective, low key lighting requires doing things to increase the contrast while high key lighting means processing for less contrast.
Many photographers seem to shoot mostly normal key images. Nothing inherently wrong with that. Great images can and are produced with normal key lighting. But just for grins-and-giggles, if you're not occasionally shooting high or low key images, you might want to give these techniques a try. If nothing else, it will be a good learning experience as well as adding variety and range to your portfolio.
The pretty girl at the top, shot and processed in a fairly high key way, is Teagan.