My country (USA) has benefitted hugely by being the reserve currency: effectively being able to generate money by fiat with lower chance of this causing inflation because other countries buy dollars and hold them in reserve to buy oil, etc.
I expect the economy in the USA will take a small gradual hit over the next decade as we lose (mostly exclusive) reserve currency status.
I think in theory, say the US Dollar weakens, everything appears cheaper, exports increase. US companies will then be able to employ more people within the country and thus improves employability and domestic consumption.
It makes us poor overall, if we consume imported products, travel internationally, and if the economic plan fails in which employability and domestic consumption does not increase. This can happen when other equally competitive countries counter by de-valuing their currency as well.
It might be an advantage for most people in the country (at least in the short term), but it would be a disadvantage (even in the short term) for the people with the most wealth, and, perhaps more specifically, for the people with the most power over monetary policy.
The advantages (particularly in the near term) that countries get from weakening currency is why the people who loan them money have come to insist than monetary policy should generally handled by independent central banks that are, while generally accountable in some way to government, also somewhat insulated from political pressure from the rest of government (and, often, with direct influence from the financial industry.)
We will be better off in the long run by not playing that game. Keeping the currency fairly stable helps to encourage long-term economic growth by allowing businesses and consumers to plan ahead. That's better than chasing a quick and unsustainable boost in exports through devaluation.
But the point is, the US dollar has been kept “artificially” strong for a good while now, which goes along with a structural trade deficit, current account deficit, low domestic savings rate, unemployment, rising prices of non-tradeable goods, and struggling US export industries. On the other side, countries with artificially weak currencies like Germany or China have had high domestic savings rates, trade surpluses, current account surplus, etc. This kind of imbalance builds up pressure over time, and isn’t stable in the long term.