What is Previz and why should we teach it?

What is Previz? Wikipedia defines it thus:

"Previsualization (also known as pre-rendering, preview or wireframe windows) is a function to visualise complex scenes in a movie before filming. It is also a concept in still photography. Previsualization is applied to techniques such as storyboarding, either in the form of charcoal drawn sketches or in digital technology in the planning and conceptualization of movie scenery make up."