Reclining Figure

I went to a Henry Moore exhibition, thought how much I would love to own a piece of his work, then settled for a postcard from the gift shop. As you do.
I find postcards from exhibitions like this an odd thing. I'm never too sure what the expected use of them is. Do most people buy these from an exhibition they see while on holiday and then post it to a friend?
Or like me, do they buy them just to keep as a memory?
It feels like one of those conventions that just exists without question. A little like my very own collection on this site. Behaviours that we undertake without thinking.
Exhibition = Sell an image on a postcard.
Background in art and design = Collect random things that make you think and that you think look cool.