Money is an abstraction to provide a measure of available resources. Obviously, multiple currencies and distinct economies do not help. You need a baseline to match the various economies. It becomes an additional concern - the way money behaves becomes an issue by itself.
Is it obvious? I don't actually understand why there needs to be a baseline currency, unless it's of a useful resource like gold or silicon or something. It seems to be problematic for a specific country's currency to be the baseline because it concentrates too much power in one place. I know China for example really wants something other than the USA dollar to be the standard.
A baseline will only work well if the economies are (or can be made) comparable or if there are only a few large economies (that rea reasonably comparable). Any differences have to be handled in some way - tariffs, exchange currencies that differ depending on direction, etc. In a small society, one abstraction will work just fine. Introduce complexity and everything will be more difficult.
So no - baseline is not a given, but it's what they are trying to do.
And multiple currencies are always a concern because they are all abstractions but controlled within separate systems.
Which is why cryptocurrencies are problematic; they introduce a variable not related to resources - server farms and the like. They are really no better than the fake money you use to "buy" things in any number of online games.
Processing power is a resource. I don't own cryptocurrency but how is it any more virtual than bizarre mortgage derivatives, stock puts and calls, and whatever other layers over layers of financial nonsense that overpaid Wall Street suits come up with?
It introduces multiple additional abstractions, including non-market dependencies. All of a sudden, the value of the currency is also tied to specific resources - silicon availability, delivery chains, Nvidia graphics card availability, etc - and yet there are region dependencies as well because things like Nvidia cards have export restrictions. It's a weird situation.