It does seem to be beneficial to advance the stories of all girls, even if you're not at all into one or more of them, as some of their stories are tied together at some point, and by skipping one girl, one could unknowingly be skipping out on content and/or just interesting knowledge of the other(s).
... Or is that not how it works? It's been a minute, and I admit I never really tried to purposely leave any particular girl out of a playthrough to test whether or not the stories of all the others would still advance as intended, so I could very well be talking out of my ass (obligatory fart noise).