Well, I'm natural and I'd better put conditioner on my roots or they will not be detangled. My guess. They are talking about those with 3a to 1 type hair that have oily scalps.
I remember watching a Macherie youtube vid and she said you "Shampoo ypur roots and condition your hair". That's how I've been doing it ever since but that is just me. I don't think it would be harmful if you did.
I always apply conditioner to my roots because detangling would be difficult.
I keep bins of conditioner for co-washes because I go thru so many bottles and I never want to go out and buy conditioner for that purpose.
I apply my condition root to tip also. I just make sure to rinse my scalp well, because my scalp can get irritated if conditioner is left on after washing.