Mr C, I tend to agree it is not worth the hastle and risk.
Will you arrive for that holiday booking?
Will you arrive where you thought you would?
If you fly back civ how will you get home from the airport etc etc?
I indulged once when I was in Cyprus. We had priority and it was over Christmas. They were very good and we got the return tickets for a Herc waiting at home.
At Lyneham they put DAC on the flight and that was that. In those days though the system counted for something and at short notice a Comet route trainer was laid on