Then I'm going out on a limb and say it's bullshit

We use 3 jaw in our CNC-lathe, and all of the other manual lathes.
The only reason you want to use an 4jaw, is when to centre something that isn't at centre by it self if you know what I mean. But then we are talking 4jaw invidual.
I have worked in workshop for 10years, and have never heard of that you're saying

My "mentor" in lathe, have 25 years of experience, and have never done otherwise either.
You may have right, but they who learn you that, must have ment something else? For what reason?