At a personal level, collecting IOUs works fine as a way to defer consumption (ie, you can save for retirement by putting money in a bank account or gold bars u

At a personal level, collecting IOUs works fine as a way to defer consumption (ie, you can save for retirement by putting money in a bank account or gold bars under your bed or whatever). At a whole-of-society level, that doesn't really work and "saving" had to take the form of warehouses full of stuff.