If the penny is over valued (exchange value > cost), forgery is encouraged. If the penny is under valued (exchange value < cost), it pays to repurpose existing pennies. [...] In the same way that maintaining overvalued fiat monies requires monopoly privilege, maintaining undervalued fiat monies require the prohibition of repurposing.
Here's the BBC profiling paper money from the Ming Dynasty. The first line of the BBC article reads:
This Chinese Ming dynasty banknote is inscribed with the title Great Ming circulating treasure note and a warning that counterfeiting is punishable by death.That is one way to discourage entry and thereby maintain the exchange value.