By DAVID GORMAN, The Providence Journal

When was the last time that you had any need for a $100 bill or perhaps a $50 bill? Indeed, most purchases that Americans conduct over $20 are in the form of a check, wire transfer, credit or debit card. This begs the question: Who has the need for the $100 bill?

The answer is clear -- the underground economy and criminal economy thrive on paper cash, especially the $100 bill.