There are reasons to want a 4K/120Hz screen....
1. Future proofing
2. Games like Ratchet and Clank that have 40fps mode (only possible on 120Hz screens) at full native 4K (only possible on 4K/120Hz screens). Not only does the game look the same as standard 4K/30 fidelity mode, but it also plays more smoothly and has much lower input lag (thanks to 120Hz) of like 8ms or something.
So yeah, there are reasons to want a display that's capable of handling a lot more than your typical 30/60fps games.
Uhhh... yeah... I agree, because I literally wrote those two things in the post you just replied to. Also a 3rd thing, being 4K60@444 HDR since HDMI 2.0 limits you to 4K60@422 unless you use dithered 8-bit output instead of true 10-bit to save the bandwidth for 444 chroma, but consoles don't appear can't do that, or the manufacturers don't want them to at least.
Then I also spoke about PC users who get a massive benefit from 4K120hz output when using high end GPUs + DLSS/reconstruction to output 4K120 for modern games, or just running older games at native 4K120hz. I definitely wouldn't tell them they
don't need a 4K120 supporting TV, as they actually would get a big benefit.
I'm saying, in his position, considering what he played and on what system (SP, PS5), not buying a TV with a much better quality image that doesn't support 4K120 for the same price as what he paid for the much lesser 4K120 supporting TV is a bad purchase, as it is for others in his situation.
Supporting an 120hz mode in a handful of games with the tradeoff of making
every game he plays on the system look much worse IQ-wise (from buying an edge-lit 400-nit TV vs. a 1000-nit FALD LCD or freaking OLED) is just silly imo, but each to their own. He could've bought a 4K60 OLED for 900 quid, the max price he wanted to pay, but bought the edge-lit barely mid range model that doesn't really support HDR properly for 800 instead.
He could've got a 4K120 OLED (B1) for freaking 999 as well. He knew what he "needed" but wasn't willing to pay for it, just wasn't a very smart individual. Anyway this is just a rant about an idiot now, not really anything to do with who needs a 4K120 display.
I agree its a good idea to future proof, I just don't think the tech is fully mature yet so don't base your purchase on it: 4K120 is 99% working perfectly across all brands now but VRR still has big issues with not being able to adjust gamma curves on the fly so you get elevated blacks, ie making redundant one of the biggest reasons to buy a high end FALD LCD or OLED.