A lot of photographers (and I mean a lot) just throw on a flash or several strobes and fire away and call it a portrait. But wait...have you seen a painting with the same light and shadow pattern on the young lady's face below(Hi Cassandra!!!) It's called loop lighting(Loop lighting is where the shadow of the nose either touches or comes close to touching the shadow on the cheek. Photographing the subject from the shadow side of the face is also a requirement of loop lighting).
It's considered one of the classical lighting styles and it is also the main style of lighting I use to make a portrait of a client. Why? Because the light pattern adds depth to the photo making it a more visually pleasing photograph. Who wants a boring flat looking photo that you get from taking your kid to a superstore?
Painters had to figure out how to make a two-dimensional work of art look three-dimensional. This was the first way.
Many of your better photographers have either studied with someone that taught them classical lighting or went to art school. This young lady is my sister, Cassandra. She is going to college and, ironically, majoring in art therapy.
This photograph was made with light coming through a window in our parent's kitchen and a white piece of cardboard to add a kiss of light back on to her hair. No fancy equipment. No expensive lighting system.