You could lower cast times to almost nothing. It does half the damage, but you can increase that again with other skills. I kill regular land dragons in under 10secs, before it would take about 2 minutes. My wind attack hits a dragon 250 damage at level 5 without the "Quick Cast" skill. With the quick cast skill it hits 190(also added the god hand skill that boosts wind.) I can use about 4 attacks though in the time it takes me 1. So in reality I'm hitting 190 x 4 vs 250. It works amazingly. It also makes leveling up MUCH faster.
Edit: You do use more MP but if you have Refresh Vials in your quick slot it doesn't really matter much.