I can see that overheat may be a problem when flying against the cheating AI planes, but in on-line fights against human pilots it is a major factor!
When 2 pilots of close to equal skill fight it out and try to stay alive too (no foolish head-ons), the fight may take quite some time. Then the one who has flown with full throttle all the time is usually the one who has to cool the engine first. Thus the other pilot gains an edge and will likely finish the fight. If one just keeps heating the engine and smokes it himself (and even lands the plane), it is as much a victory to the other pilot as a shot plane. S! to the more skillful pilot
Just to add that in games where there are more than 2 pilots, this usually needs less consideration. Situations change more often etc. But if your goal is to survive... learn to pay attention to overheat. (Actually the same goes with limited ammo... dont waste it)
... major factors... all turned on for "full real"