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Yes, I've had a couple of situations where summoned elementals were very helpful in battles:
1) A simple example: the main hero with the main army is busy with more important tasks, ;) and a strong mage without an army is, at this time, fighting off strong neutral creatures guarding some valuable artifact;
2) A hero with an army, but without resurrection, needs to break through a powerful guard protecting an artifact or a path forward; here it is important to minimize or eliminate losses of your own troops: let the summoned elementals die!
3) In a battle with a strong opponent, you can greatly ease the task by blinding, "saving for later" :) a strong stack of "infantry"/archers, surrounding them with elementals, and then attacking them: they have nowhere to go, they can't shoot, and we can shoot them, cast spells, etc.
Elementals are also useful for removing retaliation.
There may be other cases. But this ability is valuable closer to the end of the game on large custom maps, when the hero's magic power and knowledge are highly developed - otherwise, the benefit of summoning elementals will not be felt.