As in all things you need to know your tools so you can pick the best one for the job at hand. The goals for different styles vary and if you plan to shoot a variety of styles you’ll need a wide variety of modifiers.
Any light source will produce a pure white or pure black. The character if its light is defined by what is in between; how smooth or abrupt the highlight-to-midtone shadow transitions are.
The highlight to mid-tone transitions are the most important for portraiture because the front of the face contains tones only in that range. Three variables affect the character of the light. The apparent size of the source, the distance from the subject, and the transmission / reflection characteristics of the modifier.
