We don't have the full mud flap - just individual flaps behind each tire. We received no damage on our Jeep during our Alaskan trip and in the past 10 years of full timing. On the Alaskan trip we actually saw folks removing those stiff mud guards because of rocks being thrown.
This past fall we had an all-day drive on the interstate in heavy rain. Out of boredom I began watching RVs towing in the opposite direction. Those with mud flaps were having a high arc of water thrown at their towed vehicle. Those without a flap had a low spash of water. Interesting.