What is the purpose of the vent in rear fender?

Every time I travel on a dirt road, a lot of dust is entering my accent through the vent in the right rear fender. Does anyone know the purpose of this vent? I think it has something to do with the air circulation in the car ( winter/summer). I plan to block it off. Is this a wise thing to do? :confused:

the vent is so you can close your trunk without poping out a window

I have the same problem with a '93 Elantra. I'm replacing the bumper due to an accident, and while I'm at it I plan to fill in the vents with some of that expanding foam stuff. Is that OK to do? Haven't you folks had similar problems with dusty roads?