Hmm. Why wouldn't you?

Though for my travels into Vietnam, I find that getting money in the airport I land in is best (more or less same as taking money out of ATMs). I try to card my way through Vietnam, dump the cash balance at the hotel I'm staying (minus a small balance for tipping on the way out; there's no exit tax in VN airports as far as I recall) and card the rest.

I have yet to have to exchange VND back to USD.

I think my mother retains her VND. In true Hongkie fashion she rather keeps her cash float for the next visit rather than have to stop to get more VND. In the same vein she pays for twice the going rate to get our Visas from the consulate here rather than queue for VOA.