Here's a sideview.
Given the car's high performance, I would say that the rear spoiler is mainly for downforce at higher speeds and styling for everything else. It would not surprise me if there would be an aero penalty; drag-wise. I say that because the gap between the spoiler and the roofline is imposing (for downforce generation ?) and it does not follow a downwards trajectory; quite the opposite actually.
I could be wrong though. I will let the aero experts chime in on the matter.