Freeze is a versatile event that can be used both on offense and defense.  It has too many narrow-use cases to list here, but a favorite one is to allow Tundra Orcs to catch up from a scenario of lacking needed attacks. Sometimes you can’t do a certain move because you don’t have enough attacks and with Freeze you can just move aggressively anyway, freeze an enemy unit instead of killing it and then focus on the rest, knowing that the frozen unit can’t punish the next turn.  As a key bonus also that unit will be protecting you until the next turn, when you can then easily kill it with your newly gained favorable position.