Frostbrand is entirely situational. For example, you're chasing after a flag-carrier. You shift to GW to catch up, and Frost Shock to break the shift and start your attack. Well now, it's a Protection Warrior with the flag, chaining his cooldowns as necessary to mitigate your damage. Your friends haven't caught up yet, what to do? Well, instead of wasting your shock CDs on Frost Shock, swap to Frostbrand and lay waste to him. That way, Gag Order has no effect, and you can use your other shocks as necessary. Now your friends can catch up and beat him in to submission and you can get your flag back.