as I understand it, that cash is not sitting in actual bills under mattresses, it's sitting in bank accounts of some sort or other (could be short-term notes perhaps and still qualify as 'cash'). Those banks in turn invest those funds (in loans, etc) to other people and businesses. So the money isn't completely taken out of the economy - it stays in the system and is put to work (by other people). So I'm not sure how it's an actual problem for the economy.