Naturally the inclusion of more moving parts – transfer case, another drive shaft, another differential and more axles mean more friction/drag on the engine. If you’re a cautious and experienced driver than AWD isn’t necessary. But in the case of non-American automotive engineering (though I will tip my hat some to Ford’s export only models) I don’t see the AWD impact on mileage to outweigh the performance and safety benefits that Audis can give you. Just my two cents.