I'm not talking about the currency, but it's monetary value. As such, you can imagine australia and China trading in us dollars. Is free trade always beneficial

I'm not talking about the currency, but it's monetary value. As such, you can imagine australia and China trading in us dollars. Is free trade always beneficial for Australians? If you still want to consider only usd and USA and China trade. Then usd is not just for purchasing us stuff. It is also a reserve currency that china holds. It wasn't a question of currency at all, any wealth/money sent in a different economy is a loss to the original economy. A sizable gain in efficiency can offset that, but not every gain in free trade is of the required size, which is why tariffs should be desirable.