How would you damage an engine from 'over leaning'?
I can not prove that damage would happen, but I am so alert to the possibility, that I have no interest to the possibility of doing damage. Fuel distribution as quite variable, and positional of EGT probes can be quite imprecise as well, leading to erroneous readings. If I could see every cylinder indicating near identical EGT, which a belief that the probes were perfectly positioned, and the engine manufacturer recommended LOP operations, I might try it. Otherwise, the savings don't warrant the risk in my estimation.
If I'm flying an extreme long over water, I'll be looking for best range, but sure don' want to cough an engine!
I really do agree with the numerous cautions that Big Pistons has presented here (so won't repeat them). When you change the combustion in the cylinder, you can be repositioning the flame front. That can expose internal areas of the piston, cylinder head, and exhaust valve to temperatures for which they were not designed. By way of a minor (an perhaps only somewhat relevant example) what the EGT when you're doing a mag check - Does the EGT increase when one mag is grounded? Less power, why the higher EGT!
I sure don't have all the answers, and if I thought I did, the next model engine, with different combustion chamber characteristics would require a restart in my thinking anyway. During inflight and ground based detonation testing I have undertaken in Continental 470's and 520's, I have seen rapid and unexpected temperature change trends with leaning, and not a full power. These have caused me to err on the side of caution when leaning. Leaning is necessary for good engine health, and I always lean my O-200 at all altitudes (with reference to a bar graph EGT), but I still keep it 100 or so rich of peak. Fuel, no matter how costly, is still cheaper than engine maintenance....