Holy is extremely useful for adds in boss encounters that often get ignored. Using Holy against 2nd boss glider adds while in range of the boss itself is the best way to play this encounter in a speed run. On the huge pulls in Brayflox HM if the tank is smart with CD's I can spam Holy until everything dies without having to use a single Cure. Honestly you're not doing a speed run right if you're not using it as WHM.