Uhhhhhh do you know where nascar has the intake?
Its at the base of the windshield. It is there becasue the air pools and actually forces air into the intake at speed.
Now think about that and the hood having louvers and when you are driving down the hwy at 60mph. You are pushing air into the the hood and it is being sucked under the truck. You see as you drive down the road at speed a low pressure area develops under the hood caused by the ground effect the road under the truck that is not moving makes. This sucks air though the radiator and why going 70 you don't need a cooling fan. On a low riding car it actually pulls the car to the ground increasing traction and road holding.
That hood insert defeats that effect by packing the air in from the top.
Then we get into the whole steaming your windshield on the trail if you hit any water. Oil smells and stuff being sucked up by the cowl intake for the HVAC when putting around town. They don't put vents on hoods for a lot of reasons. If you look there is a seal at the back edge where the hood meets the cowl on all cars and it has a very real purpose.
Trail only stripped down truck in the desert. It is probably beneficial. A road driven truck...You may well create an overheat and a whole host of other problems.