What are some advantages of using the Euro?

What are some advantages of using the Euro?
The main advantage of the Euro is that once it is spread all over the European Union, we won't have to change the money when we travel across it.
The prices will be nearly the same in all the European Union.
The Euro will be stronger than the old money and it will compete better against the Yen and the Dollar.
And if the Euro is stronger, the euro will get richer than ever.