Last year, I was shopping for a new monitor for my PC. My 1920x1200 Samsung monitor was showing its age and the back-light started getting dim. I looked at 1920x1080, 2560x1080, 2560x1440(2K), 3440x1440, and 3840x2160(4K) monitors.
After looking at all my choices, I ended up with a 3440x1440 100 Hz Ultrawide monitor with G-Sync and an IPS panel. The ASUS PG348Q. I went with 3440x1440 for several reasons.
My first reason is the ability of the human eye to see small details. I sit somewhere between 30" and 36" away from my monitor. With a 3440x1440 monitor at the 34" monitor size, the pixels are smaller than the resolution someone with 20/20 vision can easily distinguish when they are 30-36" away from the monitor. At 30" away the human eye can see the equivalent of 0.222mm dot pitch. At 36" away the human eye can can see the equivalent of 0.266mm dot pitch. A 3440x1440 monitor is right on the edge of visual acuity for most people at that distance. Now if you sit with your face 18" away from the monitor a smaller dot pitch may help, but if you have to sit that close, you may be blind and not able to distinguish the difference anyway.