In the course of improving a process or product, you may need to utilise experiments to isolate which are the factors that are most important (remember the 80/20 rule?).
While the design of experiments is usually touched on in University, the concepts may all be forgotten by the time the student is ready to apply them in the commercial world. For a quick refresher, Wikipedia has a succinct article: http://en.wikipedia.org/wiki/Design_of_experiments