Back to one of my original question:
What if you are properly leaned (eg. ROP), cruising at eg. 5,000ft, then due to atmospheric condition changes, your RPM went up by 100 and thus causing your airspeed to increase by 10kts, you want to maintain your original airspeed so you adjust your throttle.
BUT, what about your mixture now? You have entered an area of significant atmospheric condition, shouldn't you "reset" your mixture, that is, put it full rich, then lean again to eg. ROP?