I mean a power controller. This is part of every WS2812 itself but with regular LEDs (be it RGB or not) you need power drivers for it, which I call the 'controller' too. You need to drive them at a certain amperage, then PWM them to get the right brightness. But with WS2812 you don't need to mess with power driver circuitry the OP mentioned. You just chain them to a microcontroller pin.

It was probably my use of the word 'controller' that is a bit confusing.

Yes but as far as I understand the OP is not doing that, they are just using raw LEDs with power drivers and the whole shebang that is so nicely built into the ws2812s for us. Otherwise they wouldn't need these components they're talking about.

I just connect them to a microcontroller pin and be done with it. I power them separately off a power bank (my LEDs are almost always worn, if they are static I just use an off-the-shelf 5V supply).

Yeah exactly that's what I was wondering about.

I use a few hundred at most and in those cases I just feed power at several points in the chain to reduce resistive losses in the wiring. But yeah I'm kinda interested what kind of huge installations would need that and how they work.