If China's firms were allowed to trade their dollars for Chinese Yuan on the foreign exchanges, the dollar would fall against the Yuan and undermine China's unfair 40% advantage against every American (and European and Asian) product. If they trade those bucks for some other currency, like the Euro, the dollar is still being sold and it still falls, plus China's growth draws a them right back in searching to buy Yuan, which would then rise. If China purchases products or commodities on the open markets, those dollars would still be exchanged, the greenback would drop to competitive levels, the Yuan would rise to its real purchasing power and Americans would go back to work making things.