@Star Dog , bit of an unfair comparison if you're using a smart pot , since it creates a completely different root structure.
It's not bro science .
It's basic gardening and applies to some plants and substrates more than others.
Cannabis might not be the best example , being how short it's life span is.
But generally speaking, in soil , people start in a small pot to decrease chance if root rot.
As for root structure, roots circle, they expand outward in nature looking for water, in a normal pot they hit the plastic and the receptors know they hit something due to lack of calcium. So they follow it round, creating circling.
As roots grow longer they grow thicker, that can cause choking off of the tap root.
If you look inside that circling most of the rootmass is on the outer edges.
So it goes into a bigger pot and it repeats.
And a 3rd time..
You have multiple layers of circling, more root volume, more root efficiency, in a non problematic location than if you'd just grown a plant in a single pot, because if they fill the outer edges then they end up working their way inward , eventually choking the plant.
It's called girdling, especially happens with trees .
But if you kept a cannabis plant long enough , flowering, revegging ect it could happen.
Nobody really does that though, and we would probably chop back the root zone if we did.
But it's come from centuries of humans growing plants, so it's a bit daft calling it bro science.
And you can't compare anything air pruned to something not air pruned. It's totally different