In smaller pipers such as the Warrior and Arrow it states to lean until rough then only enrich enough to allow smooth operation,
Its worth remembering that the aircraft manufacturers POH's were written around the standard instrumentation of the time. For a lot of aircraft this meant no EGT instrumentation at all.
As better instrumentation becomes available, so does better operating techniques.
When we get lambda meters the discussion of EGT will fade and we'll talk about Lambda (air / fuel ratio) readings.
Aircraft with a single point EGT measurement may have an EGT setting specified by the manufacturer designed to protect the cylinder with an outlying reading given that its known many engines have significant cylinder to cylinder variation.
If engines weren't so heavily regulated and changes were not so expensive / difficult, I suspect we'd see aftermarket intake systems that provide better cylinder balance rather than the band-aid of tuned injectors. Until then, GAMI injectors are the best option for engines that require cylinder to cylinder correction.