But, if you want to send one of those cards to someone, you have to add another stamps because the original one is already cancelled.
Recently I received through Postcrossing this card :
First day card of September 10th 1998 for the bicentenary of Tasmanian coast exploration by George Bass.
On the other side, you discover that this card is a stationery permitting a worldwide expedition from Australia.
I miss the price of such a first day stationery : is it less or more expensive than the typical first day card? Yet, it is the proof that some postal administrations remember that some collectors dare to use philatelic items in a vulgar postal way.