Unlike other manufacturers who use AIR injection pumps driven by belt off the front of the motor, Mercedes chose to use a AIR injection pump driven by an electric motor. This is what makes the clicking whirring noise when you cold start the Crossfire. Ir pumps extra 02 into the exhaust manifold to get the catalyst fired up while the engine is still cold. Once the exhaust temp reaches a certain level it kicks off. It reduces cold start exhaust emissions and serves no other function. As to why you might want to remove it...well, it's noisy, kinda ugly, sorta right in the way up top front center on the engine and really only runs for about thirty seconds before kicking off.

Slim