Meh. I start to hate that word. Powerlifters always focus on it and that's good and all but truth is most people are just weak. It's not as if they have strong quads.
There are reasons behind it.
Everyone can get to 180 squat and 200 deadlift, and then the issues start. Your posterior chain is significantly stressed by both when wanting to move on from there. As you want to improve the frequency and volume need to go up, and you need to survive overload phases.
I know many stuch at that level. 500 total seems to be the turning point. When going after that eighter you got a good posterior chain, or you get rekt. I know several guys who eat excellent, train excellent, with excellent form, but get hernia's from squatting over 180kg. That blow up their CNS when going over 220 on deadlifts. That injure their pecs from benchpressing.
These people, need to grow with higher volume. RTS by tuchscherer or variants. Sheiko, Smolov, Bulgarian will rip them apart. Sheiko is brutally demanding on the posterior chains ability to recover. Smolov aswel during the intense meso phase. Bulgarian is much less heavy, but they wont progress because the 85+% peak ech time will considerably punish the chain so that it wont improve, but barely recover for the next training.
In my experience, watching every powerlifter in the benelux that has a +600kg total, they all have at least a strong posterior chains. Us prime conventional deadlifters even more.
Its simple. People in a gym who without warmup, can walk over to someone and for teasing to a single with his +200 max and bugger off again. That is pure posterior chain strength. (i love doing that)
Its exactly the same in olympic lifting. Akkaeyev, a brutally talented -105 lifter, used to fuck about doing 300kg single rep squats without scheduling for it, "cause he liked to fuck about".
The ablity to stress the posterior chain without it remotely giving a fuck, is testament to its strength. And its vital if you want to lift over 600raw.
I heard 4 consevutive years i'd tear up my back. When i pulled that 240 squat and 285/295/300 deadlift, all i had was a sore trapezius. Wich was probably from the stand up sex afterwards.
You can get every muscle to be big and strong for isolation. The posterior chain determines how good you are for compounds.