Potterverse Familiars: What Do They Do?

[Palanan]

After watching a sad scene from Deathly Hallows Part I, the question occurred to me: what exactly are the familiars for?

When Harry is being moved from the Dursleys' to the Burrow, his loyal owl Hedwig takes a killing curse for him and spirals down into the dark, never to be seen again.

But apart from a comment about Hedwig unintentionally giving him away, there doesn't seem to be any effect on Harry. He hardly seems to notice, and there's no apparent impact on his abilities.

Likewise Ron doesn't seem too affected when his "familiar" was revealed to be something else entirely. And none of them had their familiars with them when they set out to find the horcruxes. I don't recall if there was even an explanation for why Hermione's cat wasn't still with her.

In short, the familiars don't seem to be essential, or even useful, so why are they there at all? It's been years since I read the books and I don't recall if this was ever mentioned. I notice that none of the adults have familiars, so are they some form of training wheels for the students? And if so, how exactly?

[Rater202]

Other than a one-off mention referring to a specific creature in side materials, familiars aren't a thing.

They're just pets.

Magically enhanced or bred rats, owls, and the like are more intelligent and longer lived than naturally occurring members of their species and obviously something like aphoenix has overt magical powers, but other than owls(which are trained to carry mail) they're just pets.

[Tvtyrant]

After watching a sad scene from Deathly Hallows Part I, the question occurred to me: what exactly are the familiars for?

When Harry is being moved from the Dursleys' to the Burrow, his loyal owl Hedwig takes a killing curse for him and spirals down into the dark, never to be seen again.

But apart from a comment about Hedwig unintentionally giving him away, there doesn't seem to be any effect on Harry. He hardly seems to notice, and there's no apparent impact on his abilities.

Likewise Ron doesn't seem too affected when his "familiar" was revealed to be something else entirely. And none of them had their familiars with them when they set out to find the horcruxes. I don't recall if there was even an explanation for why Hermione's cat wasn't still with her.

In short, the familiars don't seem to be essential, or even useful, so why are they there at all? It's been years since I read the books and I don't recall if this was ever mentioned. I notice that none of the adults have familiars, so are they some form of training wheels for the students? And if so, how exactly?

Fan theory a friend of mine had back in the day:

There was a series of magic wars between humans, elves, and goblins eons ago that humans lost. The terms of their treaties were designed to hamstring humanity, which is why the wizarding world is so stupid.

Wands, which make humans noticeably weaker at magic (Harry without a wand could make people turn into balloons and make plate glass disappear, with a wand he could make some sparks.)

Familiars, who spy on humans and report to the goblins.

House elves, who make life so convenient that the wizards have no reason to develop magic any further.

Dividing muggles from wizards.

[Vahnavoi]

Familiars in Harry Potter are just pets. They are sometimes highly odd and capable pets, but still, pets. They don't have any explicit link to their owners. This doesn't mean they're useless. For example, Hedwig was capable of delivering mail, so it was clearly a well-trained and useful owl.

[warty goblin]

Owls definitely do more than "just" deliver mail, since they can also locate people. Hedwig repeatedly delivers mail to Sirius when he is abroad and thoroughly in hiding for instance. They're less a postal service, and more a highly capable magical homing system.