I have worked with countless of the 75% disengaged people in organizations who love job descriptions because they can use it as a prime tool for their disengagement.
Making sense of this odd declaration begins with understanding engagement. Engaged people are continuously paying attention to what's shifting and changing around them. They work mindfully to be nimble in responding to the emerging opportunities to be of value to everyone they touch and make promises to. They are fluid in asking for and offering help when capacity and demand become unbalanced. They are always looking for ways to learn and grow.
Disengaged people don't. They rely on the minimum version of their job description to work mindlessly, defining success as lack of failure. Their use their job description, and any levels restrictions, as a prime excuse for saying no or simply ignoring most of what goes on around them. It certainly gives them permission to work without passion and outsource their happiness to others. Without a job description they would actually have to be mindful, conscious, responsive, agile, creative and proactive.