This really depends on the size of the screen. For most laptops, I'd argue that 4k is useless; 1440p is high-res enough that you get perfect clarity anyway.
For 83" TVs you obviously need more pixels to get a good viewing experience because you don't position yourself several meters in front of the screen to make the pixels unnoticable.
As an aside, many 4k/1440p videos are not really 4k or 1440p, vs how we would classify a 4k/1440p monitor. Video is mostly 4k/1440p light levels, but less than that w.r.t. color information.
In addition, common video compression techniques (at least the simple ones that I could still understand) basically reconstruct blocks of pixels. Reconstruction is lossy, at best.
If I had to guess, something similar could be done in games as part of their optimizations.
For me, there's only a difference for the text console. For GUIs I have to halve the resolution to make things usable so it doesn't really help anything.
For 83" TVs you obviously need more pixels to get a good viewing experience because you don't position yourself several meters in front of the screen to make the pixels unnoticable.