When people think of the benefits of a currency union, the first one that is usually mentioned is increased trade. I read a journal article for Dr. Greenlaw´s economic analysis class, in which the author argued that trade has not increased significantly in the Eurozone since the introduction of the Euro. Here are a few reasons that she lists: (1) Labor mobility is low in the Eurozone due to language barriers. (2)There is no common fiscal policy. (3) Eurozone countries´ business cycles are not in harmony. (4) Eurozone countries do not have the option to devalue their currencies to promote exports because they have given up monetary policy. (5) The fiscal and debt guidelines are too strict, which depresses economic growth.
An important note to make, though, is that this research was limited and more advanced research on the subject might show different results. The article is interesting and if you want to have a look, click here.