I had a good experience on DXB-LHR, booked on QF1 which was showing a 40-minute delay into DXB was able to be rebooked onto QF9 which left/departed on time. Was in F booked with AA miles. The only downside was less time at the lounges, but worth it overall in order to arrive at the office on time.

I doubt that it would have worked if QF1 was showing an on-time arrival, however.