You tune for best performance.
Knock, EGT, AFR are just aids in getting there.
Say, you make a real strong pass and see an EGT of 2,100dF. You know the engine won't last long at those temps, and to back down the tune, or if its a sudden change from last pass, something is wrong.
Same with a WB O2, from one pas to another, it reads really lean or rich, Ooops, Houston we have a problem.
With a new set up go to the track, with your WB, and see a 13:1 at WOT, you know you need more fuel.
The NB oem sensor is a switching type. Trying to read more into then that is just being less then smart. Look at how many head gaskets are blown around here. Might be a clue.
I was running a 800mv, reading at WOT, and with a WB found out I was at 12.8-13:1 AFR. Plugs read fine. Fattened the motor up and geeesh, what a difference