Originally Posted by MDORPHN
As I understand it, having the M button on closes the wastegates, thereby decreasing spool time and speeding the transition from partial to full throttle.
When the M button is off, the wastegates are open which reduces backpressure/pumping losses and increases efficiency/fuel mileage.
The above is exactly what I'd love to hear confirmation on from those who are balls deep in the DME.
I'm curious if this is true or it's all just more aggressive throttle pedal mapping.