Oh goody, a chance to display my ignorance...
At my outfit we use both derate and assumed temperature reduced thrust to reduce engine wear and save on fuel. It's common sense. You don't need 27K to get a lightly loaded 738 off the ground safely on a 3000m runway. There's also the added issue of avoiding rocketing skywards at 5000 fpm on a SID with step climbs into a busy TMA. TCAS RA in London anyone!?
However, for added safety, we also use the performance calculation figures for intersection takeoffs even though we usually use the full runway length - along with everyone else. Happily, there's (almost) always a helluva lot of runway left when we rotate.
Surely it's not an either/or decision. In the real world it's quite possible to neither firewall the engines due to some misplaced fear of mountainous terrain nor risk damage to the frangibles if you have to perform an RTO.
Where performance considerations require it, we use the full shabang. No shame in doing so. And good fun it is too.
