Past Experiences
May I, a long way removed from current operations, throw in my view.
Many years ago I was Sqn Ldr Ops at Upavon (or ASCOT Ops). I was frequently asked for a crew duty extension ("if we need it") when a Herc had been re-routed through Goose Bay before carrying on to Gander for the originally planned night stop. Strangely, we were never asked the same question if GB was the night stop. My response was always wait until you are at Goose (maybe 10 + hours away) and then see how you feel.
My second second-hand experience was during Gulf War I. I was then back at Lyneham and we had a detachment with DetCo in Akrotiri. CDT had already been extended to 19 hours for all operational flights but the DetCo wanted to have the authority to extend it further if necessary. Wg Cdr Ops thought we should let him. Mindful of the distant pressures I used to get whilst at Upavon I disagreed, saying that the DetCo would be faced with unfair pressures from possibly self-important senior officers insisting that their presence in theatre overrode all other considerations, and insisted that Wg Cdr Ops and I took the issue to the Stn Cdr - he listened to both sides but then agreed with me.
My final experience was more personal. Down at 1312 Flt in MPA we had a flight party one Saturday night. It was a reasonably sober affair, ending by 2300 (by the rules). We cleared up and then went back to the Mess to bed. At 0300 on Sunday morning (this was in the days when Capt Beaky had decided Wednesday would be the day of rest) the Stn Cdr had a Stn (Exercise) Call Out. I reported to the Flight, checked that my Gd Defence Commander had everything in hand and then retired to the Crew Room along with the rest of my and the 2 other crews to snatch some rest in case we went flying. Capt Beaky then decided to call in and was incensed that I should be resting ande not running round like the traditional blue a***d fly. That night I and my crew were on QRA and were called out at about midnight to go look for a reported fishing vessel on fire and act as top cover for the helo sent to assist. We remained in the area for about 5 hours but returning to MPA on the PAR (chosen for prudent safety's sake) I "woke up" to hear the T/D controller saying "You are well below the glide path ACKNOWLEDGE". Capt Beaky was a fighter/bomber puke and could never understand that I was one of only 3 Captains and not one of 15 aircrew as he saw it. As they say I learnt about flying from that and it is probably that that coloured my approach to CDT extensions whilst at Upavon and after.
From my experiences, it is all very well breaking the rules and getting away with it but the man who said that rules were for the guidance of fools was entirely correct. As an aircraft captain, you can always "break" them with good reason (when really necessary) but you surely have to be there after the event to defend your actions. If you are not, others will make that judgement for you - witness the never ending thread at the top.