I think if you are overclocking to ANY degree on a board that has it, then you should use it. And if your power supply has it, and your board CAN use it, then use it. But if you are running at the stock configuration and your power supply does NOT have it, then I see no reason to worry about it as you're never going to draw more power than the single 8 pin EPS can deliver at the stock speed anyhow. Now, if we make a jump to 10/20 processors at some point and the TDP is significantly higher than the current 95w TDP of the 9900k, then it may become a necessity rather than an option.
Even so, we had much higher TDP units drawing more power on previously gens and the single 8 pin EPS was plenty. Look at the 7820x. That's an 8 core 16 thread CPU with a 140w TDP, and even then the extra four pin on the Skylake and Kaby lake X boards was optional and only recommended when extreme overclocking was part of the configuration so unless something changes, or has changed, in the fundamental architecture of the power delivery system, I don't see it becoming a necessity anytime soon.
I could be wrong, wouldn't be the first time for sure, but I think that's on point.
Even so, we had much higher TDP units drawing more power on previously gens and the single 8 pin EPS was plenty. Look at the 7820x. That's an 8 core 16 thread CPU with a 140w TDP, and even then the extra four pin on the Skylake and Kaby lake X boards was optional and only recommended when extreme overclocking was part of the configuration so unless something changes, or has changed, in the fundamental architecture of the power delivery system, I don't see it becoming a necessity anytime soon.
I could be wrong, wouldn't be the first time for sure, but I think that's on point.