There is no short answer to this but you are right to some degree, what works works.
Every boat is different and different things come into play.....how old and baggy/stretched the mainsail is, rig tuning etc.
The big deal is wind strength.
The more wind the more you drop the traveller down its track. E.g if it is blowing dogs off chains, and the boat is on its ear with white water halfway up the stanchions, may be time to ease the traveller a bit

Light winds when you need power, the traveller comes up the track and above centre line. (and the main sheet eases)
too much weather helm and the traveller needs to be eased..
Its really horses for courses, some boats are sold without travellers, and some guys I have raced with are more than happy to "just leave it alone please!"