Well, in colder climes the reason we've always been given for an 'engine warm' is to put a bit of energy back into the front 2 cylinders to reduce the chances of a head cracking - very expensive
Yet another general aviation myth handed down through the years. I think John Deakin in his engine handling articles of yesteryear (The Pelican's Perch) mentioned the head cracking fallacy. If that was a reason for head cracking then you should never fly in rain because it cools down the front cylinders to the extent it causes head cracking.
