As to fairness to parents, it's having them live with the scenario they agreed to when they were together still.
As to the kids, it keeps thing as stable as possible for them.
I agree. We all have our opinions regarding parents so here's mine.
Children NEED their momma when they're preteens but as teenagers, they definitely need to leave mamma and use Dad as a role model. This includes both guys and gals. There's nothing a daughter wants more, as a teenager, than her fathers approval. Same for the son.