After having experienced a 4x4 being thrown by the wheels on our last MH, I personally can tell you that the hanging guard does its job. If it wasn't there the 4x4 would have went through the radiator and out the back and into the toad. Instead it was forced out the side from under the rig without damaging anything.
It bent the **** out of the flap. The flap was still there when we sold it. I have never had any rock damage on from the flap throwing up rocks on the last 4 toads we've owned.
The flap on our last MH and this one were about 2" from the road when aired up.
I will never remove ours.