If somebody just starts up (in a piston) and flies straight off with a cold engine, they are IMHO nuts. I see renters do all kinds of stunts (not least because they are getting billed brakes-off to brakes-on) but I would not do it in my own plane.
Could not agree more, but this was something which had never been mentioned to me until only very recently. Having flown with about 7 or 8 different instructors none of them ever mentioned anything about letting the engine warm until my IMC instructor just made a comment about it in conversation. It was also mentioned during my ATPL course, but I don't remember anything at all about it in the PPL exams.
Problems with students and new PPLs doing checks at the hold can be caused by the way their instructor teaches them. When your fairly new to it all you tend to just copy what you have been told instead of thinking for yourself, to point you will try and get into the exact spot you were in when you where shown by the instructor.
It took a while before it dawned on me that there was no reason at all that I could not do the power checks on the apron instead of the hold, the way the aircraft get parked means there's nothing to get damaged, pre take-off checks (take no more than a few seconds) still done at the hold or on one of our runways the hold point is so far away from runway they can be done when rolling to line up.