Speculation: Shortens up the long side transfer tube so less heat is lost to the engine bay; meaning more is available to produce boost. Should also improve throttle response. If the kit or install is very well worked out it will equally space each cyl's exhaust pulse to the turbo so that there is a constant & even pulsating exhaust flow in the normal operating range. Sort of like tuning header tube lengths to work best in a given RPM range.