Leadership is about finding the way. When you know where you are heading it's easier to convince others to follow you on that path. Nobody wants to follow those who are lost. By knowing the way you don't even have to take that path yourself, but that's not what the real leaders to.
Picking up the path doesn't necessarily mean going where you as a leader want to go. It's not your job to lead your team to your destination. No, you need to find the path for your team. Guide them where they need to be regardless your own destination.
Actually, all leaders need to know is the destination and how to get there. It's the scouts job to find that path. Maybe there should be a position above leaders: the scout. I've seen enough "leaders" without a set direction I'm sure there would be a huge demand for such service as well. But wait! Isn't that what the consultants do?
Anyway, knowing where to go is a huge help for everyone who aspires to be a great leader.