From Good to Great:
Most answer that budgeting exists to decide how much to apportion to each activity, or to manage costs, or both. From a good to great perspective, both of these answers are wrong. In a good-to-great transformation, budgeting is a discipline to decide which arenas should be fully funded and which should not be funded at all.
In other words, the budget process is not about figuring out how much each activity gets, but about determining which activities best support the hedgehog concept and should be fully strengthened and which should be eliminated entirely.