Suppose China and the U.S. each produce 10 tons of steel. GDP PPP would consider both economies equally sized (and they arguably are), but nominal GDP would favor the U.S. because steel costs more there. GDP PPP is more useful if you want to compare standards of living or consider consider a country's ability to sustain a war for example.
That's the positive argument for PPP that I'm already aware of.
Thing is, to quote @YZF a way up chain: "There is no quick decoupling from the USD." — I'm curious about the dollar itself in this case, rather than about the goods.
