Anyone who has witnessed a forest fire understands that it has a life of its own. These are the furious fire elementals, just as much a force of Nature as any river but much less predictable.
As with most level 2 and 3 summoning spells, the number of Fire Elementals you can summon with this spell probably isn't enough to really affect the battle. Don't cast this unless you're short on ranged capability and you don't have any better summoning spells available.
Fire elementals are ranged units, and preserve is a bit weak on those. That being said, both Water Elementals and Waspworts can provide better damage at range. But if you have neither of those you might want to give this a go.