mmmm
Presume your talking about "all wood" bows
Well, here is our thoughts!
When you first string a bow, it will probably shoot its fastest, due to it having the least amount of string follow!
As the bow starts to follow the string and takes it's follow, then the bow will settle down. The Bow will shoot with its best consistancy at this point!
The more the bow sets, and settles down the less it will set the next time you shoot it, the more consistancy you will get. Untill the day it will consistantly NOT shoot, if you get what im saying...
This all depends on the design of the bow, and the quality of the timber used, and the strain the bow has been put under during tiller, and shoot history. Includes arrow weights, draw length, bow length, Wood from the top of the tree/ bottom tree. South/north side of the tree. List goes on!
Sorry to be vague, but wood is wood.