Look at it this way:

If it's too lean--you'll deadstick and possibly ruin the motor.

If it's just a bit too rich for maximum power, but stil pulling good and flying the plane like you want-- then 2 things wil occur
1-it won't die
2-you won't ruin it

I see guys tweaking the high speed needle for everything it can give and then they wonder why their engine dies. Hmmmmmmmmm [sm=spinnyeyes.gif]

And I see guys tuning so rich that it won't spool up and drag the airplane off the runway.

Find a happy medium and err to rich. Your engine will last longer and you will avoid a deadstick--in which case--the airframe may last longer too. Depends on how good you are at deadstick landings.