Very good question Les! I didn't fully explain at the related post. Here's how I understand it.
When the aim is to develop primary branches, you can defoliate everything to slow down the overall growth and keep the internodes short.
Because full defoliation is so stressful, you can expect some interior branches to die. This doesn't matter when developing primary branches as typically only a small section of primary branch will be added during each growing season. The secondary branches will come later.
Short internodes is what matters when building primary branches and fully defoliating a tree is a great way to apply the brakes and produce shorter internodes. That's the "science" behind it: more stress = shorter internodes which is a good thing when developing primary branches.
Partial defoliation is used when you want to preserve weaker, interior branches. This is generally the case on more developed trees where balancing vigor is important.
Here's a case study for when not to fully defoliate:
And here's the same tree partially defoliated a few years later: