Leaders aren't always managers and vise versa. It is a rare individual that is both of these things. They have very different skill sets, both critical to success at a high-growth business.
Understanding who your leaders are and who your managers are will help you create an organizational structure that not only addresses core business functions and needs but also morale and culture, which are equally if not more important. It will also help you identify where there might be gaps or people in the wrong "seats on the bus," to quote Jim Collins.
Leaders have a unique ability to rally employees around a vision. Because their belief in the vision is so strong, employees will naturally want to follow them. Leaders also tend to be willing to take risks in pursuit of the vision.