[makomk]

As people have pointed out this means that the US or wherever can print money and controls your monetary policy, but that's actually the least of the problems. Euros and US Dollars in large quantities, and digitally transferrable versions of them, can essentially only exist as numbers in databases controlled by the US and EU government respectively. So by adopting them as your country's currency, you're effectively giving them control over your money. They get to decide whether it continues to exist, whether you get to access it, whether it gets transferred to some well-connected megacorporations in those countries that bribed your former leader into a dodgy deal... In short, it gives a whole bunch of control to powerful entities who have tended to use their powers in ways that have not been good for developing countries at all.