I lean depending on the a/c I'm flying.
If I have a fuel flow gauge or EGT (that actually works) I will lean as per POH/instructers training (providing >3000ft in single, whatever specified in a twin)
I am much more dubious if the a/c doesn't have either, I am not a fan of leaning till the engine splutters then riching the mixture slightly, I do not trust the reliability of this method. I nearly had an engine cut once using this method. Some clubs teach you to do this purely to keep their costs down.
Certain types have fuel vaporisation once an engine cuts if the engine is warm, that tends to prevents an easy restart.
I wouldn't lean any single below 3000ft either way, to give myself a good choice of landing options if the engine cuts.