For general use, a decade-old computer is probably fine, it's only when webly things start to not work that its prognosis negative. For laughs, I'm writing this on the 2009 Mac Mini - most websites still seem to work fine, other than the average local newspaper site, which will kill anything.
Mobile OS are of course, reliant on app developers continuing to support older apps (and the financial model beyond hobbyist apps doesn't encourage that).
Games need right-there, right-now performance so they push the envelope. Dealing with hi-definition video is still a load, especially at 4k and above, though with modern graphics cards you can mostly do this is in real-time without too much sweatbreaking. Print and digital imagery isn't even an effort – and I remember the good old days when applying a Photoshop filter meant you could go make a cup of tea, drink the tea, have a chat, make another cup of tea, pop to the shops to get some more biscuits, and come back to see it was still at 78%.
We do bigly data science which mostly requires a lot of memory, a machine that moves data quickly, but only reasonable processing power, but then it's generally down to how long do you want to wait for it to complete and is it worth paying more to not wait so long.