I know this is going to start a lot of controversy, but leaning properly is better for the engine then just leaving the mixtures forward. Every type of engine is different, so it is impossible to make a blanket procedure. It also helps to have cylinder head temps for each head. To simplify it, when you pull the mixture back, it is true that you have less fuel to absorb heat so the temperatures rise, but then pull it back some more and then there is less fuel to make the fire burn hot. The reason so many people don’t like this is because the engine will start to run rough and shake off its mountings. If that happens, you have a poor fuel system. If you have a good fuel injector system, this should not happen.

If you don’t believe me, hunt around the internet for lean of peak operations. I believe John Deakin had a big series on it on AVweb.