2weels - it largely comes down to the natural range of human vision.
The central part (the fovea) having a range of about 55° (I've seen figures ranging from 40°to 60°), binocular vision combined of ~114°, and a peripheral range of ~160°. Read any of the Wiki articles on the human eye as a good place to start.
This is interesting
https://petapixel.com/2012/11/17/the-camera-versus-the-human-eye/
You want the Fov of your binoculars to be well corrected and reasonably sharp most of the way to the edge. 70° AFov is regarded as where extra wide starts, and is about the current limit of well corrected, reasonably light full size binoculars with sufficient eye relief for glasses wearers. Some prefer even wider fields and are not too concerned by softening at the edges, though if you want to maintain the ER, then weight (an expense start to climb). Non-glasses wearers (and short eye-lashed folk!
have a bit of an advantage here.
Consequently anything less than 60° AFov is usually going to seem constricting and tunnel-like. My preference is for a sharpish to the edge AFov of ~70° but then again I wear glasses and like a lighter full size bin.
In an 8x bin this would be 154m @1km, so at a close distance of say 10m the field you can see is only 1.54m (5ft) ..... it doesn't take much for a little geewhizzit to suddenly flit 3 feet away and out of the field of view so that is why people prefer as much Fov as they can reasonably get. It also comes in handy for watching a couple of circling raptors at close range without losing one or more off the edge.
Have a look at the Nikon MHG in 8x .... one of the best wide Fov compromises on today's market.
Chosun :gh: