Though PDFs are impressively flexible and useful paper-replacement files, many people and businesses are simply more comfortable printing physical copies. In some cases, with larger businesses, universities, and other organizations, that can mean ridiculous amounts of paper used and discarded for little reason. The environmental impact of paper is a contentious topic, one I'm sure will be discussed passionately in the comments (i.e. theoretical sustainability vs. illegal logging and optional governmental "guidelines"), but anyone that's worked in an office knows how much unnecessary printing happens on a regular basis.