It is only the authority to do so, the at will be taken away from the various national banks and given to the European Central Bank
This is to prevent some countries especially the more powerful ones from making policies, which would be to the disadvantage of other less powerful countries in the same region. In other words, to provide a fair trading and business grounds for countries within the European region.
You would enjoy bank loans or lending with less interest rates. The financial market would also be widening hence reducing financial costs. A wider consumer base will also be provided for your goods and services, but you must also be prepared for very stiff competitions.