system
A chat on subreddit /r/pcmasterrace
human
I think "needs" is overstating it. For games that won't run natively at 4K just use the resolution slider / upscaling options. Games that don't have either option are probably old enough that you won't need any help with a recentish GPU.

I have a 4K monitor and TV, but rarely actually play at native 4K. To which someone might ask, why not just get lower res, cheaper displays. Well it's still useful to have those extra pixels for other uses, like work, watching films, things like that.
gpt
Reading text is a big one. After using any 4k monitor, text on a 1080p monitor looks like a blurry mess