One big benefit is that it elaborates on Kylo’s motivations for turning to the dark side, which we never really get in TFA.
I mean, it’s clear Kylo was seduced by the dark side; even in the original trilogy, all we get is that Vader was seduced by the dark side. Not saying that the “why” or “how” doesn’t matter, it’s that “seduced by the dark side” is enough of an explanation.