at low spell speed high crit dh it could be worth it i guess but even then your gonna want those extra fire 4's across the whole fight.

as others have stated there is times when you could skip its cast to get extra fire 4's before something jumps away or dies.

probs most sensible place to skip it would be with leylines up but then your running a higher risk of missing a tick and losing casts.

overall having a smoother rotation with all elements lining up is better than a more random mp tick rotation.