I usually change from D to S when overtaking on a single carriage way. It's got the quickest response and means that you are over the line for a shorter time making it actually SAFE mode
Seriously the quicker you overtake the less dangerous it is for anyone involved. No real need to use it at the lights/dual/motorway as the 4.2 V8 has plenty of grunt and acceloration and you've always got kick down on the pedal if you need that OOOMPH!