It is, of course, possible to cope with unexpected shocks and policy differences under a fixed exchange rate or a monetary union. But the adjustment process will take longer, will be more difficult, and will cost more overall.
Imagine the adjustment in our economy that would have been required in 1997-98 in response to the fall in commodity prices, if the Canadian dollar had not been floating. To maintain a fixed exchange rate throughout that period, much higher interest rates would have been necessary to resist the downward pressure on our currency from the falling receipts for commodity exports.