If the friend is purchasing the ticket from DL with a credit card, be aware that there's a possibility (depending on the route, with certain international routes considered high risk) of needing to show the credit card that was used for the purchase to DL at check in, with a possibility of the person who owns the credit card doing this in advance at the airport (or a DL ticket office, if any still exist). AFAIK this might also apply if a credit card is used to pay the taxes and fees on an award ticket, again depending very much on the route. Most airlines do this an an anti-fraud device.