They do the exact opposite in the Danish military, here we're trained to hold our breath if we need more accuracy, and in my experiance it works, it really steady's my aim, and is especially apparent with a scope.
That's not what it's there for though.
Thing is, video games are limited by the screens we play them on, in the real world you have about 180 degree's field of view, and stereoscopic sight at an amazing resolution.
No ordinary screen can give us that in a game however (you'd need a home Imax format screen or something), the lack of clarity (pixilation) is one thing, but much worse is the lack of periphial vision it gives us.
For this reason, games are unrealistically zoomed out, we play them at a "fish-bowl" distorted view so as much periphial view as possible can be crammed onto the small screen space, which is good, we need to have some periphial vision to play.
But it comes at a cost, since we're zoomed out, everything appears smaller than it really is, and add pixilation, and the lack of true stereoscopic sight to the problem, and it makes judging distances in games, not to mention seeing anything with any clarity at range, very difficult indeed, unrealistically so.
This is what aim-zoom tries to fix, you shoulden't think of it as a zoom, but rather, as going from an unrealistic zoomed-out view to normal, because that's what it actually is.
The fov you see when it's "zoomed-in" is normal human sight, it's what you came from, the "zoomed-out" view that was unrealistic (but a nessesary evil, because without it, we'd have none of the periphial vision we would have in the real world).
Technically speaking, having aim-zoom is more realistic than not having it, because it allows the game to mimick two real things about human perception, that we have good perihial vision, but also that we are good at judging range and the clarity we're able to see with, it lets the game simulate both thease facts (but sadly, not at the same time).
The downside to it as that, in order to simulate both thease things, you have to use two sepperate FOV's, and zoom in and out between the two, which, of course, does look rather silly, there's no denying that, it does look a bit silly.
But you should think of that as a nessesary evil, a result of the technical limitations imposed on us by the screen, it's not perfect, because the hardware we use to view the gameworld is not perfect.