Since 3440 x 1440 consists of around 5 million pixels and not 8.3 million, it’s a lot easier on graphics hardware than full 4K. But at the same time, it’s still over nearly three times the resolution of full HD. That’s a gaming sweet spot. Which is why ultrawide 3440 x 1440 gaming monitors routinely achieve over 100Hz native refresh rates for reasonable prices. Meanwhile, most 4K gaming monitors still stick to 60Hz unless you go for more premium models.
Opting for a 3440 x 1440 screen means you can get excellent game performance out of mid-to-high range graphics cards like the RTX 2060, as opposed to the much more expensive RTX 2080 or RTX 2080 Ti you’ll need for native 4K at similar framerates.