In the Harry Potter universe, why are spells that can affect lots of targets at once used rarely?

Question

Following up on the question "What curse did Peter Pettigrew use to kill thirteen muggles at once?", how come large-scale spells are quite rare / not used often in the Harry Potter world?

Off the top of my head I can recall:

• the fire snake scene in the room of requirement
• Dumbledore fighting off the inferi at the Horcrux-lake
• the defense shield in the Battle of Hogwarts

Pardon for not remembering the details, surely someone can chip in to correct me if I called something wrong.

Why are large-scale spells not used often, especially in many-on-many battles?

One possible explanation is that they're simply too difficult for a single wizard to manage alone. The defense shield over Hogwarts might be a sample of this, as, if I recall correctly off the top of my head, it was a lot of small spells, not one large spell.
However from the first reference in the above list, we might see a counter-example, as Goyle isn't generally shown to be the mightiest of wizards, yet he creates a large-scale inferno.

We can see that Dumbledore, possibly the greatest wizard of his era, can manage such spells even after being severely hurt (see the reference in the list above), wouldn't other wizards of similar scale, for example, Voldemort, be able to use such spells to fight off a number of enemies at a time easily?

If there are any canon explanations that would be great, but logical reasoning will do as well.

Answer 1

I think it's interesting that you bring up Goyle's fiendfyre spell and the large-scale inferno that he creates using it, considering the main cause of that was his inability to actually control the spell, and he nearly killed everybody in the Room of Requirement (which included himself) as a result.

That's probably the reason spells like that aren't used very often. They're difficult to control, the results can be absolutely disastrous if you don't have full control over them, and even for powerful wizards like Dumbledore or Voldemort, the potential for collateral damage is pretty severe.

The only large fight scenes we see are chaotic, with enemies and allies all over the place, so there would be no way to use such a spell without also hitting those on your own side. It's entirely possible that Voldemort would have used such a spell if he was fighting a group alone with no nearby allies, but I don't think we ever see such a fight in the books. Even Voldemort seems to be against wasting magical blood when it can be avoided, as evidenced at the end of Deathly Hallows, so I think even he'd avoid needlessly killing his Death Eaters as much as possible.

As far as defensive spells go, like those on Hogwarts or the ones placed on The Burrow at the start of Deathly Hallows, they seem to be more of a combined effort by a number of witches and wizards (The Burrow was protected by the combined might of the Ministry of Magic and the Order of the Phoenix) rather than a single wizard. Hogwarts also seems to have some very old protective enchantments that can be controlled by the Headmaster, but details are pretty lacking.

Essentially the reason we don't really ever see them used is because we never see any situations where it would be feasible to use them.

Answer 2

I think it is the result of a few different reasons.

• The ability to actually control these spells takes a very powerful wizard they are not normally used to harm a lot of people but more so to overwhelm an opponent in a duel. For instance the large scale fight between Dumbledore and Voldemort both used large area spells to try and overwhelm the opponent.

What happens when an ordinary wizard uses powerful magic:

"Like it hot, scum?" roared Crabbe as he ran. But he seemed to have no control over what he had done. Flames of abnormal size were pursuing them, licking up the sides of the junk bulwarks, which were crumbling to soot at their touch.

• I think that it is pertinent to mention that wands allow the wizard to focus magical energy to a point this would suggest that magic in Harry Potter is built around magic being precise. All the main spells we see are used on single points or single targets you'd think a mass Avada Kedavra spell would be around if it was feasible. Other pointers towards a precise magical continuity in the universe is just how to cast a spell every flick of the wand and letter of the incantation has to be perfect to get the right result from the spell.

• It seems that to cast a large area spell it has to be worked up so you have to gather the, let's call it magical momentum. Whilst gathering the MM you are open to an attack from somewhere else. Normally you don't have one wizard versus say 30 it just doesn't seem to be done like that in the wizarding world take Dumbledore and Grindelwald I'm sure many wizards saw the duel but clearly none helped. In a battle I think it would be different but during a battle collateral damage would be too high. Most wizards good or bad would probably apparate away before being overwhelmed enough to even risk an area spell.

• Area spells tend to be that an Area not so well targeted as in popular RPGs with finite ranges etc they seem to be reckless. I doubt Wormtail cast a spell to kill 13 muggles it also isn't known if he cast a spell like that at all. It has been theorised he used a spell on a gas pipe to cause the explosion.

• Very much like what Antony Grist said in his answer with protective spells we only have examples of numerous wizards casting together. It can also be assumed that hogwarts protective enchantments were placed by the four founders. There is one protective area spell which would be Harry's Protronus in Prisoner of Azkaban.

And out the end of his wand burst, not a shapeless cloud of mist, but a blinding, dazzling, silver animal.[...] He saw it lower its head and charge at the swarming Dementors.

This may effect a large area or multiple enemies but I personally would call it focussed magic.

In the movie however there is definitely large pulses of magic which stop the Dementors.

Answer 3

Let's assume two types of spells for this: The focussed spell (ex: a huge fireball/explosion that is bound to hit multiple people) and a split spell (i.e. a spell that is fired at multiple targets at once in different directions).

Focussed spell: Judging by a few of the books (#5 - battle at the ministry & #7 - battle at Hogwarts) wizard battles are pretty disorganised and the fighting happens all over the place. This means that casting AoE attacks might do more harm than good (it targets everything), so it is (usually) not very opportune to use them.

Split spell: Firing a single spell at multiple targets at once would not be an easy feat. The same result could probably be achieved by firing the same spell at multiple targets in rapid succession (instead of all at once). In book #5, when the ministry tries to arrest Dumbledore, he was able to stun the lot of them in the blink of an eye. Wether he used a 'split spell', or simply cast spells in rapid succession, I cannot say, but the effect is about the same.

General reason: they might drain the caster much more quickly, and in a battle it is important to keep your stamina up (outlast your opponent).

Answer 4

In a few words

1. so far as we know there are no "area of effect spells", or at least none of an offensive nature. There a wards of course but wards are mostly protections though some wards are surely deadly against would be aggressors and some wards could be used offensively.Imagine what a derivative of the bubblehead charm could do, if expended on a massive scale and tweaked to create vacuum instead of supplying air! What's more, "true and lasting curses", those we see in fairy tales don't seem to exist for instance a wizard in Terry Godkind's Sword of Truth Series curses red fruits to poisonous.

2. You're thinking like a muggle. When you think about war you think about mass troop movements, artillery,Chemical attacks, the Atomic bomb... Wizards don't think on those terms. Wizards Duel, and that's what they do. They fight one on one most of the time and move on to the next enemy or go support an ally if they survive the Duel.

3. Indeed if there are "area of effect" spell we don't know about" they must be particularly diffcult to cast and only the most powerfull ans skilled wizards would be able to cast them. Plus Pettigrew coul've simply send a blasting curse on the ground killing a dozen muggles with shrapnel. There must be many spell that when used in creative way can have wide scale effects.