The specific transaction process is that when swiping it, the real-time exchange rate of USD against AUD will be used to generate a USD amount on your card. If you repay in USD, nothing will happen.

If you repay in RMB, you need to exchange USD against RMB on the repayment day.

It's hard to say whether it is worthwhile to draw it, because the foreign exchange rate is quoted. If you swipe your card and make repayment at the same time, you use RMB for repayment, your card is USD card, and you pay Australian dollar. The currency of this transaction is: Australian dollar-USD-RMB. If you go this way, you will directly lose a little exchange rate difference against RMB than Australian dollar. This difference is usually not big, unless you are in a big business. But usually your repayment is a long time later, which depends on how the exchange rate goes afterwards.