The act of using one currency in the world mean's that every country in the world uses the same currency.
The use of a global currency will be the starting point of eliminating suffering in the world.
All nations would certainly benefit since there would no longer be currency risk in international trade. Traders would no longer fear for currency fluctuations.
Economically developing nations would also benefit base on the introduction of a stable currency, which would form a base for future economic development. For example, Zimbabwe suffered through one of the worst hyperinflation crises in history. The Zimbabwean dollar had to be replaced in April 2009 by foreign currencies, including the U.S. dollar.
It has gotten to a point in life where global currency is now needed in the world in other to end constant inflation and suffering in different countries.
When there is one generally accepted currency in the world, inflation and poverty will no longer be one country fight but a world fight.
If it was gradually eased into place and the proper nurturing took place, a global currency would actually save a whole bunch of waste from happening each year - but the manufacturing costs are rather small in comparison to the sovereignty over currency that many countries prefer. You might in fact compare it to the gold standard, which turned out to be a failure in the end because supply was too limited in comparison to demand. Finally you might run into the final predicament, which you could see in places like the Eurozone which merged together into one currency. For a while afterwards Germany got very rich from other countries weighing the currency down and Greece was able to borrow like crazy on credit backed by Germany, but this created a dangerous cocktail that would have to be addressed.