When attacking, I can seperate the attackers into two groups, the main assault and the rearguard. A good time to do this would be when you have 4 regulars and 2 dunlendings. Main assault is 4 regulars, 1 dunlending. Rearguard is 1 dunlending. Even if the attacker gets 5 hits, you'll still have a leftover Dunlending, since you can't lose units in the rearguard no matter what.
But if the battle goes more than one round, you would rather have the extra troops, right? Seems a bit pessimistic to expect your opponent to get 5 hits in one round.