Chainsaw Question/ Curriculum?

Looking for clarification on what this means? Any info/feedback appreciated.

First thing that comes to my mind is just a regular old notch with holding wood? Some describe it as 70% backcut 10% holding and 30% face cut. Others say to cut 1/3 of the way into the tree (same thing) or to cut 1/4 into the tree (slightly different thing). I see no reason that this is bad for firefighting- so Iā€™m wondering if they are referring to something else or just suggesting a different ratio?