Actually, what you're all talking here is metalurgy. It is more beneficial to have the engine run more than not. This keeps the number of expansion/contractions of high presure/low tolerance components to a minimum. Which is even more important than just temperatures. Mainly, it is consistent temperatures that increase engine life, and, just like an old car (even new ones but we all need instant gratification) these engines will have seriously reduced wear on them by allowing them to "warm up" for a bit before givin it the juice for T/O. Tha one engine that sat cold until just a minute or two before t/o will have the more signs of wear than the one that has time to "warm up" before hitting the pos n hold.