If the same currency, then the game will certainly be beneficial. Reduce a lot of unnecessary costs, will be a lot more money to invest in other projects.
Having several currencies do not really means having high costs, it is just more uncomfortable to have to use so many different currencies all over the world, but the advantages of having several currencies are great, a country without its own currency will be unable to print its own currency and all its debt will be in the currency of another nation if the country were to get in a huge debt it will be unable to escape its compromises through inflation since their debt will be in the currency of another country.