This card is needed if you are a foreign teacher in China. Its main use is by you/your school to change part of your salary (up to 70% monthly) into hard currency. This is their verification and your proof that the exchange has taken place.
At one time, the card could be used for discount airfares/train fares in China. This was because fares for Chinese and foreigners differed greatly. Fares are now supposed to be equal and the card has no real effect in travel rates. It might help in some hotels.
(Chinajob.com October 18, 2006)
