The best managers are the ones that add value to the organization. They don't just assign work, make sure people show up for work on time, and tell people when to get their assignments finished. They are also invaluable in identifying how to do work smarter, how to become more productive as a team, and how to align the work their team does and the skills their team possesses with the actual business goals and directions of the organization.
But the longer a manager serves in his or her role, the more likely that fatigue will set in; management will erode to the point where the manager gives up his or her strategic vision and eventually goes through the motion of making sure people show up for work on time, assign work, and make sure that assignments are finished on time.