Say there's a battle that is a sure victory 3/4 yellow in your favor, but you have a unit that is low on health. You will lose that unit from the auto resolve, so what you do is fight the battle and shove that unit to the rear. This happens often enough to warrant a new feature!
in my opinion we should have an option on the battle deployment screen to select any unit and remove them from the calculation. Maybe something as simple as double clicking the card greys it out.
Alternatively we can just adjust the the auto resolve function prioritize healthy units in the fight and only use weak units in the most dire odds.