The two most distinct advantages in the Benz application are easier plumbing/fitment and the reduced intake tract volume. The entire intake tract volume is pressurized as boost rises, so increasing that volume results in unnecessary lag. With an air to air system it is quite difficult to route the larger diameter air hoses as opposed to the smaller diameter water hoses. The water to air radiator can also be much thinner than the air to air core and so fitment while retaining A/C is much easier. You can also get better cooling with an optimally designed water to air than you can with an optimally designed air to air system. I did air to air on mine and it was enough of a PITA and enough of a compromise that I would opt for air/water next time.