Originally Posted by ND76

This is the option to use if your trip is solely on Delta (and its regional partners) and you've got SkyMiles in your account. You get full MQMs (as well as bonus MQMs if you buy F); the last time I checked you don't get MQMs with the ordinary "miles + cash".

I frequently use this method to secure F class on flights where I would have a slim chance of getting upgraded as a PM (such as any longhaul flight to the west coast). I think you get a much better deal this way.