Oregon has a biennial budget, so some Oregon employee predicts how much money Oregon will earn over the next 2 to 3 years (which is basically impossible to do), and then Oregon leaders have to come up with a spending plan equal to or less than that revenue estimate.

However, Oregon's costs have no relation to the revenue that the state predicted it would get, so it is constrains the solution space when unforeseen costs or cost trends happen. For example, Oregon predicts a certain amount of revenue, but gets 3% more than the predicted revenue, but that is because prices for everything went up 3% more than expected, now Oregon has less money than it needs to pay its expenses (since it has to return any revenue which was 2% over the estimate).

Oregon is the only jurisdiction I have ever heard of with this kind of strict refund law, and its rigidity seems to be the main issue, along with the 2 year forecast requirement (since forecasting even 1 year is hard enough).