This has been done to death, but it's pretty simple really....
On a PC monitor curved isn't really necessary until you start getting to 34 inches. For these, like the superwide x34 the subtle curve is mainly to mitigate against IPS glow in the corners, an unfortunate side effect of IPS tech and more noticeable with a big screen if you sit near to it.
You could also argue that it's slightly more 'immersive' with a curved screen, when sitting right in front of it.
For televisions, when you're sitting way back like most people do (8-9 feet in the average UK home?), a curved screen is absolutely pointless, and is really a marketing gimmick.