Right now, your $100 bill is equal to the $100 in the bank. If you're bank account has a 5% interest rate, you earn $5 of interest in a year and that $100 bill is still worth $100. But what would happen if that interest were -5%? Then you would lose $5 over the course of the year. Knowing this, you would rationally withdraw the $100 ahead of time and keep it out of the bank. This is where the separate currencies come in.
Read more: http://www.businessinsider.com/electronic-currency-2013-11#ixzz2lKPxOPNE
Read more: http://www.businessinsider.com/electronic-currency-2013-11#ixzz2lKPxOPNE