If you look closely you'll see it changes the direction of where it sends the airflow. Upper part of it is just another flap in those barge boards, with a slot energizing the boundary layer on the inner side to keep it attached. Then in the middle it start going outboard, to send the lower layers of airflow coming under the nose outboard and towards those many slots and leading edges creating a bit of downforce. Basically, it brings more clean and high energy airflow exactly where it's needed. Almost text-book stuff really