Nichrome explained it well. Normally, each installed card is allowed to draw up to 75W via its PCIe slot. Of course, a lot of graphics cards need way more than that, that's why they have seperate PCIe connectors. And actually, they tend to draw way more over the extra PCIe connector on the card than via the PCIe slot. Why do they do that? To not overwhelm the ATX power plug, because all PCIe slots are powered through the main 24pin ATX power plug. So let's say a graphics card needs 150 Watts total under load, then it might draw 120W via its 6pin PCIe connector and just 30W over the PCIe slot.
The graphics card makers already calculated with the 24pin ATX power having a limited amount of total wattage supplied to the board. So they make sure to draw most power over the seperate 6-pin or 8-pin connectors (or combination thereof) on the card itself.
Now, in the rare case that you have several quite "thirsty" cards in the PCIe slots, which disregard that consideration for the total 24pin ATX wattage and each draw the maximum allowed 75W each over their PCIe slot, then and only then would the PCIe 6-pin connector on the mainboard alleviate some of that high power demand from the 24pin ATX plug, and distribute it more evenly with the help of the second cable.
Similarly, for the two EPS12V connectors next to the CPU, the second connector is only there to spread the load, so to speak. When you have well over 300W power consumption of the CPU, which can only happen during OC, the second EPS12V plug comes in handy. You basically double the width of the cable and reduce resistance and load on each cable and plug, so they get less hot. On the mainboard itself, the connectors are combined again and feed the CPU VRM.
Lastly: Depending on which CPU you got, CPU overclocking is pretty much out of the question with Rocket Lake. Due to the four different, very aggressive turbo modes of the top-end CPU models, those CPUs are driven to 99% of their capabilities once you remove the power limits and give the turbo modes free reign. For the last 1%, you will have to live with an exponential increase in power draw and heat production, which can quickly overwhelm some of the best CPU cooling available.
Intel went right to the edge, especially with the 11900K. They went above the normal efficiency range of that silicon for this halo product, so it behaves - at stock, with power limits removed - like a substantially overclocked CPU would have behaved in the past. Meaning, the power draw is very high already, and the efficiency is quite low. If you still try to go above that with OC, you will see that the performance will hardly scale anymore, but the power draw and heat from the additional voltage required will rise incredibly steeply.
What's more, even RAM OC is largely limited to DDR4-3600. I've been extensively testing my own new Rocket Lake system this week, and i can tell you that DDR4-3600 is the new sweet spot. Because above it, you are forced to enter Gear 2 mode, where the memory controller runs with half the frequency of the RAM, which causes a serious performance loss. So you have to go way above DDR4-4000 to make up for that, which just isn't worth it. Just like on AMD, it's now best to stick to 3600 and optimize the timings.
Just so you can't say you haven't been warned
