You don't need to take away people's purchasing power to encourage them to invest. If an economy is growing, there will always be higher returns in investment than in holding cash. Monetary expansion encourages unsustainable consumption and debt accumulation. Why is this preferable to saving? When people save, they don't do it with the intention of one day dumping the money in a lake. They are still going to use the money, just on a longer time scale for a better-considered purpose.