Top layer of perlite???

I was over at my buddies' house checkin out his setup, and I saw that he had a layer of perlite on top of the soil. I would have asked then and there but he's kind of dickish about having to explain shit. what is the purpose of a layer of perlite on top of your soil???

I'd say it was there to help with drainage

I'd guess to help maximize root growth closer to the surface of the soil.