[Theleb]

Its not an increase when compared to imp immolate, and its incredibly situational - Imp Immolate is useful all the time for Fire Spec.

I never even use lifetap tbh (well, not as much as I could - certainly in DPS sensitive fights its not something I do for preference) its a marginal benefit to have Cataclysm with proper groups and chain-chugging mana pots - and as you need Immolate in a fire rotation its a better increase than Cataclysm, no question of that.