I'm not sure it's the manager's responsibility to compartmentalize and then assign/distribute work to each employee. Aren't people happier and more productive when they're in charge of their own destiny?

I view the manager's role as one that clearly defines and communicates business imperatives and facilitates communication about how to get there. If you're telling people exactly what to do, how does that enable them to do great work? Aren't they just doing what the manager tells them to?