Most countries have their own currency. In effect you are asking why each country has its own currency.
Historically each country has always had its own currency and run its own economy for its own benefit.
The EU is one of the few parts of the world where there is a joint currency used in multiple countries, and the only example amongst economically advanced counties.
In theory we may eventually have a common world currency. This would require agreement between all countries to set up a joint international body to regulate the currency (as the EU already has with the 'European Central Bank'), which is independent of any one government. I don't see this happening any time soon.
The biggest savings is in trade between one country and the EU, or between the EU states. Conversion of currency is complex and needs a vast accounting system. Businesses would need to hedge against currencies if they sell products in different countries that use different currencies. One common currency in the EU makes this process much easier. Another advantage to the EU states is the power of their currency as a reserve currency for the world. A currency held by many states is more attractive as a reserve currency as the market for the currency is more liquid.
They now share the Euro ( European Currency like US dollar.)
Antarctica has no national currency, while the US currency is broadly recognized as a currency benchmark for work economics.
euro
EUros
the euro
EU, I think means euro, like the currency of Europe €
If EU represent EURO currency, the advantage is that in Europe many countries have adopted EU for transactions. Tourists and travellors need not exchange currency.
Hungary joined the EU in 2004, but has not yet joined the Euro currency.
to unite different countries under one universal currency, therefore bringing peace one step closer.
Franks.
The euro is the current Italian currency. Italy is a member of the European Union. Use of the euro isn't a requirement of EU membership. For example, Sweden is an EU member that doesn't use the euro. Italy is an example of an EU member that does.