I would think with more spirit it becomes less and less useful, not more and more useful. Basically I really, really do not see the point to using CS at all except maybe during run phases. Possibilities:
Zor'lok attenuation phase: You had a lot of spare mana and you weren't really able to cast so you can CS him. Problem: It's not like you really needed the HP to begin with (even when it was current).
Durumu maze phase: You aren't really able to cast so you can CS him while running + HS. Problem: Poor use of mana versus just casting for the HP anyway, and this is a (possibly) mana-intense fight especially when learning.