Breaking Ifrit's horns greatly reduces his damage output. It's really useful if achieved in the first 25% of the fight. I haven't parsed or anything, but I can definitely tell you that with no horns broken, I would take ~100-150 damage on top of stoneskin from Vulcan Burst, and with both horn broken, it wouldn't even eat through SS.

Just from eye estimates, I'd say his damage output was reduced by 30% (1.7k down to 1.2k on some attacks). This is not useless unless you just go in to speed-battle him.

I really do like procing !!s in Abyssea for drops, so I wouldn't be too against them reincorporating this, but honestly endgame loot probabilities are supposed to suck.