1440 vertical pixels in a 34" 21:9 monitor means you usually don't have to worry about whether your software can adapt to a non-standard DPI. At about 109 DPI, it's the same as a typical 27" 16:9 panel, just with more pixels off to the side. The density is a bit higher than the typical ~94 DPI of a 24" 16:10 display, but the difference can be tolerated by most users. Jumping up to 140 DPI (32" 4k 16:9) is enough that you either need exceptionally good vision, or you need to compensate through software scaling adjustments or major ergonomic changes.
27" iMac has been 2560×1440 from 2009 until they went retina in 2014 (and they're now double in both dimensions, so same logical resolution).
At arm's length, on a 27" screen, 1440p is very practical. Getting more screen space than 1080p is what bumped me from 21-24" screens, and it fills my vision enough that if I jumped to 4k I'd either be moving my head back and forth with a 40" screen, dealing with even smaller UI elements, or wrestling with OS scaling.
