I don't think I've seen a situation where it
hasn't been effective. It has the right level of intimacy to go
just beyond an implication into something meaningful. And that's really helpful considering 99% of romance in manga is just
"JESUS CHRIST JUST TELL THEM ALREADY! WHY ARE YOU DOING THIS TO YOURSELVES!?". I think it's the precise balance of intimacy and subtlety that gives it that... je ne se quoi. And the phrase is beautiful in and of itself, particularly when given the meaning it has.
...of course, it
does require that the recipient understands what it means, which Chika very clearly didn't.

(I do love the way Riko explained it to her, though. In a way, that made it better and more effective than if Chika had understood the phrase immediately.)