If stoich is correct, and your entire fuel model and air models are correct, you should never have to adjust your tune even if you add some heads and a cam.
Just bump up idle and enjoy.
Commanded AFR should equal actual and you wouldn't have to make any other adjustments minus possible spark adjustments.
Granted you adjust stoich to reflect the actual stoich of your fuel.
The right way is to have your air and fuel models as accurate as possible.
The 3800 way is to do whatever the **** you want and just keep tinkering until you get what you think is acceptable.
Honestly thats just a stupid way to tune, but its what a lot of the "3800 pros" do.
Reasoning? No idea. However based on what I've seen, it forces you to go back for adjustments, resulting in more business.
But if the tuner told you that would happen if you changed something, then you'd think they're right, and trust them and continue to pay.
When in reality, nothing could be further from the truth.
Oh well, continue doing whatever makes you happy. Thats what tuning is about right?