I did it once, but not intentionally. How abusable it is I don't know. I was renewing my Costco membership at the service desk using my rebate check but was $3 short of the total amount. I gave the clerk my cash card, figuring they could take the $3 off of that. Instead (and without even asking!) they cashed out my $300 cash card and took the $3 in cash. Manager said it was the only way to do it.

YMMV.