If you don't allow the currency to float, your import/export ratios can't respond to market forces, and in a globalized economy this can be catastrophic, especially during a global downturn. To quote from the wiki:
"One of the junta's economic moves was fixing the exchange rate in the early 1980s, leading to a boom in imports and a collapse of domestic industrial production; this together with a world recession caused a serious economic crisis in 1982, where GDP plummeted by 14%, and unemployment reached 33%"
Of course, you can't prove a counter-factual. There's no way to know for sure what would have happened if they hadn't done this. But it seems to me that this, at least somewhat, mitigates the significance of this particular example.