Why and when should a champion take PTA?

Its mainly for champions who can proc it very quickly and either arent interested in attack speed at all or just dont care as much about attack speed as they care about quickly dumping some damage. Renekton and Pantheon can both apply very quickly with their empowered W's and get some massive burst damage if paired with the correct items, Akshan and Lucian can also apply it very quickly with their passives and dont spend as much time purely right clicking enemies as most AD carries, Viego can also do it very fast with his Q passive, to name some examples.

For melee champions though the traits that tend to make them good PtA users also tend to make them good Conqueror users so the majority of melee champions prefer Conqueror over PtA in most cases, which is worth keeping in mind since Conqueror is generally better in a prolonged fight. For burst builds though PtA tends to win out. The exposure damage you apply varies in usefulness, in a laning phase where you just proc PtA in a short trade and back off it does nothing, but in a fullall in fight from max health or a teamfight where your entire team follows up on it the exposure damage can end dealing even more damage than the proc.

The general thing you are looking for though, again, is the ability to get 3 hits in quickly, BUT not benefitting much from attack speed, making it a somewhat specific pick that's less generically good than some of the competing runes.

So PTA is good in in situations where ur likely to be hitting the enemy champion alongside an ally (jg or adc). Or you really want to take prescion tree as your primary because all the minor runes are really good but ur champ still prefers short trades (think voli) .

As far as HOB is concerned champs that prefer hob over pta even if both are usable are champs that can proc something with autos but that proc isn't repeatable for long trades(trist e, varus w pop, quick stacking passive for twitch E). All those champs could go pta but it's not very useful for how their short trade patterns go and if they wanted to go for long trades there are other runes that are just better. But compare those abilities to akshan or vayne passive where those things will continue to proc over and over again, trust and twitch E's both have cd's so it doesn't matter that hob also has a CD because you just playing around that initial ability.

For one thing, the PTA damage bonus also applies to your allies. You can also proc PTA by using abilities that apply on-hit, so it can be activated pretty quickly by a lot of champs.

If you don't have a 3+ AA passive to proc or really high AA-based damage, PTA gives you some extra early damage and team fight utility throughout the game. You often see PTA on duelist junglers, since the Precision rune tree has a lot of nice pickups, and PTA can make ganks more successful.

Laner duelists and heavy skirmishers usually take Conqueror or LT for extended fights and trades.

Something like a Renekton mid gets a ton of utility out of this rune, athough this is just because of the insane synergy it has with his empowered w, which hits 3 times for massive damage. Typically I only take pta if i know I can go prowler's claw and full ad, which just lets me burst them faster.

Renekton mid might just be an outlier though, I'm not exactly sure, since renek almost always starts his combo with an empowered w to fully proc pta for the rest of his combo.

In the case of Kindred which I use for Jungle

It synergizes well with Kraken Slayer as well as her E. It allows for pretty surprising burst while increasing damage output on a target.

PTA works well for champs that can proc it very quickly. You wouldn't use it for a Jhin since he has a fixed attack speed and that there are better runes for him like Fleet or DH

PTA gives almost the same damage as Electrocute but actually scales better.

You take it when you

• want a bursty playstyle

• can easily get in 3 autos (have auto resets)

You pretty much only take it if you have a way to proc it quickly, e.g. Pantheon W, Rene W, Ezreal Q, MF Q, Akshan E, Lucian passive, Viego passive.

early game focused rune, gives you access to precision tree while having good early damage, precision tree is completely better than domination for most champs

PTA is a great Keystone for champs with single-target aquisition and have combos or tools that allow them to, for lack of a better phrase, press the attack. Quintessential PTA users are Teemo, Lucian, and Vayne. All are very auto attack focused, don't really do any aoe stuff, and have a tool to stick to the enemy (W, E, and Vayne's entire kit respectively).

One advantage that hasnt been mentioned is that you can hold PTA so that it is available when you need it the most and has half the cooldown of HoB f.e.

Urgot

Hate to say it but… TEEMO

The burn damage after getting the pta proc is a nice trade.

One of the only examples that comes to mind right now is Neeko, who sometimes wants it in an AP on-hit build because she can auto and use W to kite well, then once PTA procs she can E+Q+auto spam for a lot of boosted damage.

Champs who have a lot of damage come from abilities but can also flex auto attack focused builds, and who really rely on murdering the frontline in front to back teamfights (damage vulnerability is going to be way more helpful on tanks than squishies that get blown up anyway). It does seem like over time this rune has become wayyyyyy less popular than it used to be. It used to be THE default ADC rune if you didn't know what else to take. Lethal tempos range extension when changed shifted that pretty heavily if I remember correctly