When I first got started in photography it seemed that everyone needed five lights in the studio to take a professional, salable portrait. Main Light, Fill Light, Hair Light, Accent Light, and Background Light. After feeling that I sort of mastered working with all five, I started turning them off one at a time until I found myself doing a lot of one-light and two-light portraits that I personally loved and so did my clients. I felt more free, moved more quickly, and felt that creatively that I was doing more interesting work.
In a world of confusion in terms of how to make the best exposure in the studio there is one very comforting reality whenever you work with one light source. What you see is what you get. This is not always the case whenever you introduce light number two or three or four. Model lamps will vary, distances and brightnesses will change. But with one, you see what you have and can make an appropriate adjustment if needed.
Whenever I work in the studio my exposures are fairly simple. I aim the dome of my light meter towards my main light source from the subject's position and simply do what the meter tells me to do. With my old trusted friend, the Sekonic L758DR, if it says the exposure should be f8.0.7 that indicates f8 2/3 or in digital apertures, f10. Often people forget to read the small number after the main aperture number when using a light meter. Being off on my exposure by two-thirds of a stop is a pretty big fix for later and I'd rather get it right when I shoot it.
Certainly working with numerous subjects you will want to introduce more lights and often even when working with one person. But if you can master the art of one-light photography, everything else becomes a lot more simple. Even working with window-light is one-light photography. Just pay close attention to placement of the light.