Stimulus that comes too late will not help support economic activity in the near term, and it could be actively destabilizing if it comes at a time when growth is already improving.
Thus, fiscal measures that involve long lead times or result in additional economic activity only over a protracted period, whatever their intrinsic merits might be, will not provide stimulus when it is most needed. Any fiscal package should also be efficient, in the sense of maximizing the amount of near-term stimulus per dollar of increased federal expenditure or lost revenue.