Cruise control is excellent on m/ways for improving mpg, unless there are lots of hills and traffic. When you use it you realise how much other people slow down and speed up over time for no other reason than they are not a computer but are very bored and not concentrating very hard, which is understandable. What on earth zero air resistance has to do with it is anyone's guess!?!?
Yes, but equally I could say what has love got to do with it?