Flashguns and strobe lights aren't just for capturing perfectly exposed subjects, they can be valuable as creative assets too.
When you first start out using lights in your photography, the aim is typically to create images that are properly lit. That might mean they are low-key or high-key portraits, but the lights you use have one purpose: to illuminate the subject. Once you have that mastered, it's worth looking into what else can be done with lights.
In this video, Daniel Norton conducts a shoot for Adorama in which he practices different advanced lighting techniques. There are many methods that could be called "advanced" lighting techniques, but my particular favorite is using a strobe to create a multiple-exposure image. The original method for multiple-exposures was to expose twice (or more) times on the same section of film, resulting in two images in one. With digital cameras, you can do this in-camera by shooting in a dark location and keeping the shutter open while you use a flash or strobe to light your subject(s) a few times. This will capture them in different positions, all in the same file. Yes, this could be done in post, but it's not nearly as fun.