Boxsters do not have a "wing". It is a spoiler. It provides down-force when it raises (automatically at about 75 mph), with less drag than a wing.
According to the owner's manual: "The rear spoiler reduces air resistance and, particularly at high speeds, reduces rear axle lift."
Some people don't like the way it looks, but it is effective and efficient. Aerodynamically it works much like a
Gurney flap, with the rear of the car.
*I left the window open too long before replying and didn't see all the other replies. ...Beat that dead horse