US government should be required to balance its budget annually because current spending levels are unsustainable. Creating a balanced budget is a sound money management practice that will certainly help the US government manage the money it collects better. It would also help in making the government priorities more visible.
It is already required of states to balanced their budgets annually. People have to find a way to balance their budgets, or they won't have anything at the end of the year. The federal government should be held to the same requirements. As government programs become needed, we should always find a way to pay for them. If a program is important enough to pass and implement, it important enough to fully fund. If not, then it should be left by the wayside.