It was used more than once but not many more times. The British used it at Goodwood and, I think, Totalize, there might have been a couple of others associated with the Caen battles. The US used it for Cobra. In addition to the mess it made of the terrain, the friendly fire casualties from bombing inaccuracy were also a problem. That too isn't represented.
It was actually used a fair number times (Cassino, for example), enough that I knew someone who was taught the German doctrine on how to survive being carpet bombed.  However, it is too powerful in the game. I suggest one change: An air unit can carpet bomb a hex only if it is using atomic bombs or if a cooperating land unit exerts a zone of control into the hex. Every use of carpet bombing I can think of was against troops in the front lines.
(I have some other changes I would make, but this is the essential one, and can be implemented by players of MWiF.)
 Get in a shallow trench, so that splinters from bombs hitting the ground will miss you. Do not get into a deep trench -- it will collapse on top of you. I think that you were supposed to put your hands over your ears, and keep your mouth open. but am not sure of that.
I thought I knew how to play this game....