There are many ways to light a portrait. Lighting a portrait depends on multiple factors: the person themselves, the mood you want to set, the final use of the photo or what your client requests. At the extremes are very hard light and extremely soft light. Hard light is bright and direct, think of the big, blazing ball of fire as the sun sets. Soft light is diffuse and even, think of a totally overcast sky at mid-morning.
Most of my commercial portraits are shot indoors and I use a variety of tools to create whatever light I want for my subject--hard, soft or anywhere in between. The soft light in this shot of the model is a fairly complicated studio setup but works for this beauty/fashion image; the hard light of this editorial portrait of a University professor is from one simple strobe head and a 7" reflector. Whether simple or complex, the trick is to match the quality of the light you want to use with the type of portrait you want to shoot. It's all about the light. Determine the light you want to create then consider your options, hard, soft or somewhere in between.