As with most level 2 and 3 summoning spells, the number of elves you can summon with this spell probably isn't enough to really affect the battle. If you have enemy walkers tied down with quicksand, you might want to summon a few groups of elves to increase your ranged offensive capability. Remember to wait until you have summoned a large number of elves before shooting any arrows, as summoning more creatures doesn't increase the available ammo, and shooting with the small number of elves you start with might just be wasting arrows.