[Freon]

Removing the cowl does exactly the same thing as the risers in terms of screwing up air pressure and airflow in the engine bay. It removes the seal that exists between the base of the windshield and the engine bay that is there by design.

Look at the top front (front in terms of the car) edge of your cowl. There is a weather strip all the way across that seals against the hood so no garbage/leaves can fall from the windshield area into the engine bay, and so there is a decent seal for purposes of maintaining negative air pressure in the engine bay for proper airflow through the radiator and intercooler. If you take the cowl out there is no seal, just a huge hole from the base of the windshield into the engine bay. That weather strip isn't there to be pretty. It's functional...

I don't think this mod makes any sense, and wouldn't recommend anyone doing it. You can spend the 5 minutes it takes to remove the cowl when you really need to get in there, and its not enough weight to make a difference in terms of performance, especially when you're probably negatively affecting radiator performance which will have a more significant impact that the cowl piece that might weigh 8-10 lbs?