put in the design to reduce turbulence and swirls of the incoming air so the hot wire can accurately respond to air flow and develop the correct resistance to send to the ECU to determine CFM, etc. The MAF hot wire resistance was calibrated with the screen. Also the screen will stop things that get paste the air filter box like? You can leave it off and probably suffer some small loss but I doubt SOTP driving could tell the difference, would probably need a dino to detect.