@P_M
Cold or Hot has nothing to do with friction, oil is sufficient for that, and your theory is just a myth.
Its very hard for me to explain but I'll try my best. When you warmup your car while idling, the pistons will seat itself into the cylinders without any load, when you start driving, the load will try to seat itself into the cylinders in a particular direction, thus leaving marks on cylinders and weakening your oil seals and rings. If you do the opposite, like putting load on the engine while cold, it'll always be seated in the right position and this definitely enhances power and life of your engine.
I hope you understood what I mentioned, and believe you me, I'm not making it up, I remember one scientist explaining in an article long time back about what are myths and which ones are not! I just remembered a few facts.
Another thing you must remember, engine perform well at a certain temperature and to achieve that temperature you must drive it as it heats up quicker while driving rather then idling!