Totally agree John T.
I used to fly the bigger Cessna piston twins and always leaned them back to 'perceptible' roughness;i.e. gently pulling the mixtures back to the 'estimated' position and then very gently to the first sign of the engine note changing at the same time monitoring the EGT gauge. Once I had established the point at which the roughness started I would then richen them up '2 clicks' as per the operating manual. I do recall that sometimes it was very difficult to establish exactly the point when the roughness was starting, in which case I would do it as well as I could then richen '3 clicks'.
It may well be worth noting for those new to the game that it is important to lean off the mixture and not just fly around fully rich (which I have seen a number of people do in my past) as this can lead to fouling of the plugs which isn't the best way to run your engine either! Does depend on how high you are intending to fly and temperature etc etc.
PP