Brutal Force is a utility event that has two main uses. The first use being to assassinate the enemy summoner and champions (either by toying around with them or removing a blocker for a Frost Shaman shot), but it can also be used to make it easier to trigger Frenzy and Primal Fury. Additionally, it can sometimes be used to move a high life unit from a safe position with a Frost Shaman so another unit can finish it off.
Remember that if Brutal Force allows you to do a third attack that otherwise you wouldn't be able to do, it's worth it, 1 magic x 3 dice worth of attacks, or even 2 if it means killing a potential threat, is a good trade in Summoner War's economy.