I agree it's not an exact science with so many variables existing for each individual turkey. Understanding when to call and when to be quiet, even if it means only scratching in the leaves, is the key. I do know as a whole I typically call less than I used to. Once I gain a gobbler's interest, I want to pressure him to commit by his anxiety of what the hen is doing...why is she not coming or did she leave? And as mentioned, your set up is very important....don't give the gobbler an advantage. Unfortunately, even after many years of chasing them, the ocassional "bonehead" decision on set-up choice still occurs, and it irritates me beyond mention.
And GobbleNut pretty well summed it up perfectly.