Developing the budget months ahead of time means that you are making decisions based on projections.  If these projections turn out to be wrong, it could mess up the budget.  For example, what if we project unemployment to be 3%, and instead it turns out to be 6%.  That would mean that there would be less revenue coming into the treasury and more benefits being paid out. 

The Act created Budget Committees in each house, the Congressional Budget Office (to provide Congress with its own source of budgetary and economic information), and set standards for how impoundments can occur.

A deferral is a delay in spending and a recission is a cancellation of spending so (B) is incorrect.

This is the only choice of funds that are controllable meaning that the Appropriations Committee sets a budget each year.

B) deficit reduction

Gramm-Rudman-Hollings, Budget Enforcement Act, line-item veto, etc. have all been promoted as mechanisms to control the budget deficit.