Delegation of authority is based on the idea and proven fact that a manager or supervisor can not perform all the tasks assigned to him/her on his/her. This is simply impossible and that's why a manager has a pool of people organised in formal structure (some as Deputy Manager, Assistant Manager, Team Lead, Project Lead, Workers, etc.). A manager will delegate authority along with the respective pieces of task to his/her reportees or subordinates. In this manner, manager gets the work done. This is why authority needs to be delegated.