http://lifehacker.com/5320196/use-the-s ... -purchases
When considering a purchase, picture a stranger offering you [the cash value of the purchase] or the item in question. Which is of greater value you? Which would you choose?
If a stranger were to come up and offer you $3 to not buy that cup of coffee you might reply "Thanks, but I'd really like this cup of coffee." But if your response over a bigger purchase like a new HDTV set or a computer would be "Hmmm $800 would be a pretty nice credit card payment..." it's probably best to put your funds to use fixing more immediate problems.