"Brutes are unstoppable. They, and their hero, are immune to freeze or knock-down."
Brutes have a tremendous amount of health and damage, but are limited in their squad size. They and their hero are immune to any of Freya's freezing abilites, and cannot be knocked down.
Brutes are a good choice for when you don't want to worry about where an opponent has placed their ice wave or fireball, as they will be able to cut through any obstructions of this kind that your opponent has built into their plan and quickly disrupt whatever defence forces have been sent to clean up.