I heard some rumors of people rabidly defending the power of familiars during the pf2e playtest, however, this diverges significantly from my own play experience.

What are the usual, concrete combat uses of a familiar, assuming using specific familiar abilities, and assuming no specific picks or combo?

After taking a (well-deserved) jab at summoning, I think it's only fair I dive into what I believe is a subgroup of spells that serve the purpose people incorrectly pin on summoning. You've seen the title: I'm talking about illusions

So illusion, unimpressive right? sure it might be cheaper, but giving the enemy a free save to completely ignore "the thing" I just created sounds like a big drawback, right? Well no, wrong, unless the spell specifically calls out a save on spell cast, the "default" rule for illusion effect is

Disbelieving Illusions

Sometimes illusions allow an affected creature a chance to disbelieve the spell, which lets the creature effectively ignore the spell if it succeeds at doing so. This usually happens when a creature Seeks or otherwise spends actions to engage with the illusion, comparing the result of its Perception check (or another check or saving throw, at the GM’s discretion) to the caster’s spell DC. Mental illusions typically provide rules in the spell’s description for disbelieving the effect (often allowing the affected creature to attempt a Will save).

If the illusion is visual, and a creature interacts with the illusion in a way that would prove it is not what it seems, the creature might know that an illusion is present, but it still can’t ignore the illusion without successfully disbelieving it. For instance, if a character is pushed through the illusion of a door, they will know that the door is an illusion, but they still can’t see through it. Disbelieving an illusion makes it and those things it blocks seem hazy and indistinct, so even in the case where a visual illusion is disbelieved, it may, at the GM’s discretion, block vision enough to make those on the other side concealed.

Now that sounds like cheating. The usual summary of illusion effects without save is "it's real until proven otherwise" and proving otherwise MUST take an action. Ramming through an illusory wall doesn't count as disbelieving the illusion meaning it can still be used to cover or hide.

After this brief summary and after a cursory read through the spell list, you might think that no-save illusion spells aren't probably that common, or otherwise on the weaker side that designers didn't feel the need to make their combat use impractical, well, you'd be partially correct, very few illusion spells are saveless (and therefore, real until proven otherwise), however, those are everything but weak. I have made a short selection to prove my point:

• Ventriloquism + Invisibility 4
• Silence 4
• Illusory creature (the REAL flank buddy)
• Illusory object (the REAL body blocker)

Ventriloquism + Invisibility

Not weak and ventriloquism? isn't this spell just a gimmick? Arguable, in most cases, but that's excluding its interaction with the undetected status provided by invisibility. Using invisibility makes you undetected, but a creature can seek to try and pinpoint your location by sound or other methods, but what if you've been chanting all your incantations 30ft away from your real location? At the very least, this will prevent you from having your condition downgraded to hidden from casting spells, or if the GM is generous, allow you to remain undetected while the enemy believes you're hidden in a square you're not and waste actions trying to interact with something that's not there! Plus, it's a 10-minute 1st level buff, so just get a cheap wand for it!

Silence

It stops almost all spells from being cast, drop that on the barbarian with No Escape and observe as you've just effectively incapacitated the enemy spellcaster, with no save nor incapacitation trait

Illusory creature

If you like summoning for its flanking, blocking & soaking buddy potential, then that's the spell meant to do that. It only costs 2 actions upfront, can be sustained forever, so you can realistically ENTER every combat with it, and has scaling offense and defenses matching your spell DC instead of PL-5 statistics at best. Sure, it dies when hit, but that's significantly harder due to higher defenses, and so do most summons, or it can be disbelieved, but that's ALSO an action and only "kills" the creature for the disbeliever, leaving it free to harass everyone else

"I cast wall of stone" Illusory object

First spell rank/level wall of stone, that's it, I said it. Sure it can be disbelieved as always, but that's eating an action, and until said action is taken, the wall is real until proven otherwise (plus, I don't know about you, but if the boss wastes an action on a 1st level spell, that's a slowed 1, worth it). You can probably be even more creative with it, but at the very least, you can get an insane amount of battlefield control right from character level 1 instead of having to wait for level 9

Do note that all of those effects DO NOT HAVE the mental trait, and therefore work even better on mindless creature if your GM roleplay them as mindless (not "animal intelligence" mindless means mindless, as in, about the same level of awareness as a Roomba) then they would be extremely unlikely to try to disbelieve your illusions unless programmed to do so, which I would likely call bullshit on, so yeah, you can probably just turn the floor into lava and "win" knowing that the creature doesn't have the mental capabilities to know there isn't actually lava there and is probably programmed not to kill itself by, you know, jumping into lava

So if you guys haven't been using save-less illusion spells yet, you really should. Especially if you're occult and have access to virtually all of them. If that feels too strong to be true, probably, but it has survived since the release of the game without errata, we'll see in the remaster of course, but it seems like illusion was meant to be a very (the most?) powerful tool in a caster's arsenal so don't sleep on it!

Granted, not everyone might see them as good, and a lot of people's opinion probably comes from other people talking about them rather than experimenting with them in a real game.

Without going into details, and save for the few early levels, during which you might have seen a few skunks being conjured to great effect, a top-level summoning slot brings up a creature between 4 and 5 levels below the party.

Due to how encounter math works, a creature of this level is counted as between 0 and 10 XP in the rules for building an encounter as its chances to hit are too low to matter against the player (-5 to hit against +5 to all defense at a minimum, often more from proficiency upgrades).

Of course, that's for abilities targeting defenses, surely I just have to pick things that don't target defenses or satisfy myself with spawning an annoying flanking/body blocking buddy? This is correct, some very select support-oriented monsters, like the Satyr or, in an undead campaign, the Deathless Acolyte can give an amazing boost for their level in a vacuum; but that's before considering what truly seals this pan of the game for me

It's woefully action intensive for the caster. A good way to see it is to say that you're spending 3 actions to slow 1 yourself in order to add a level -5, stunned 1 monster on your side of the board, and if the support action of a Satyr might feel pretty good, is it really compared to other uses of 1 action for the caster, like using a composition cantrip, an appropriate metamagic, or using a well-chosen skill action like bon mot or demoralize? and that's excluding the initial 3 action opportunity cost you could have spent on a more potent spell

In short, there is a reason why level -5 creatures don't count in the encounter budget, and while a well-chosen one might impact the fight positively, 2 of its actions are almost never going to be better than 1 action of a creature 5 levels higher;

Of course, that doesn't mean the spell is useless, out of combat in the blood lord adventure, for example, a single cast at 4th level of animate dead can be used by the Wizard to heal everyone for 20 + 3 x (2d8+16) to distribute on the most injured in a minute with a deathless acolyte; that's amazing, and notably way more than the 0 a wizard would be able to provide otherwise. Similarly, if you know something is booby-trapped and you don't want to risk your rogue, a Crawling Hand will happily eat and "disarm" it for the party for the cheap price of a 1st level spell.

Summoning was specifically defanged in combat, probably as a design concern about minion spam that was prevalent in previous editions, so just... don't use it in combat and demoralize/bon mot every turn instead, you'll be doing more good for your party