system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't the whole world switch to one currency?

What would happen if it was attempted?

EDIT: Why so many downvotes?!?
gpt
The advantage of multiple currencies is that if one country has economic booms or busts they can tweak their currencies so they are worth more or less to either slow down or speed up their economies. 

Take Greece as an example. If they were still on the Drachma, they could devalue their currency and make their exports cheaper for other countries so it would get more people back to work.