It's bailout time. The moves seem to have calmed markets in both countries, and it is to be hoped that they will work in the long run, too. That lesson was ignored because fixed rates have such clear attractions when things are going well.
Businesses can enter into contracts with foreign companies with confidence about exchange rates.
The fixed rate is supposed to discipline governments, which learn they cannot simply print money to get around problems and therefore must make the tough decisions needed for economic stability. All that is true enough. When a crisis arrives, people start selling the currency to the government, which obligingly buys it and drains foreign exchange reserves. In Argentina, the government uses a currency board to assure that one peso equals one dollar. That policy helped end hyperinflation a decade ago and remains popular.