When I was working retail (almost 20 years ago :[ ) we imprinted more often because of a failed magstripe, than a computer outage. In the event the card couldn't be swiped, you could key the number in, but the printer would create an extra-long signature slip instead of the normal kind, and we'd imprint the card onto it, as proof the actual card was there. This was I assume to prevent us from having to pay a higher 'card not present' interchange fee, and in terms of fraud, made it really obvious if someone was doing something shady like typing in card numbers without the card or cardholder being present.