Originally Posted by
prgboy
I am glad the discussion in this thread re-started nicely.
As for the benefits, this is what I can think of: If you are using Delta credit card, you earn miles for twice the amount spent with Delta. ($200 spent earns you 400 miles with a Delta booking, but only 200 when booked with KLM.)
I think the flier also earns MQDs for such a purchase in order to qualify for a status. (Typically an American who stays in Europe but does not have a residency… yet flies a lot within Europe.)
Sometimes, credit cards offer good bonuses but it must be spent with Delta; my AMEX now offers $75 back when you spend $250 directly with Delta.
I think of the benefits in miles collecting as well - if the flight had the DL flight number, all booking classes would earn 100 % bonus miles, not only a fraction as when flying on AF/KL code.
DL coded flights earn MQD/miles based on fare paid, not mileage flown. There's no such thing as 100% mileage earn on DL coded flights since they don't earn miles based mileage flown. A $100 base fare DL coded flight will earn 500 miles base (5x base fare) whether you are flying 500 miles or 2500 miles (assuming it is not a DL Basic Economy fare which earns no miles at all). Likewise, it will earn 100 MQDs regardless of distance flown. Assuming DL could sell these flights as DL coded flights (which they can't legally do due to cabotage regulations), whether or not there is a MQD/mileage earnings benefit to booking as DL coded flights vs. AF/KL coded would vary based on fare paid, fare class, and distance flown. You'd probably get some benefit from being able to book as DL coded due to short distances involved for intra-Europe. But on the cheapest fares, the differences will not be all that profound (and for DL BE fares, the advantage would go to AF/KL since DL coded BE fares earn no miles/MQD/MQMs).