There has been loads of debate on or off. One mentioned that it was fitted as a method of noise supression particularly for the Swiss market. In California they usually leave it off. Drip tray certainly until it fills up and stone/dirt protection. Not sure about the aero unless you are pulling 150+. One thing you will notice with it off, if you go through a puddle with the heater on you get a cold blast for a few seconds. I'm always fiddling so it's one thing less to remove.