Magnification and tracking movement
Rifle scopes and spotting scopes each have their intended purposes. A good rifle scope and act as a spotting scope in some situations, but not everyone wants to have a 50mm objective lense on their rifles. Sometimes when I’m going to be shooting an AR15 that is setup with iron sights, I use to bring one of my rifles that had a 3-9×40 scope and just use that for spotting. The more I’ve progressed as a shooter, the more I realized that it would be nice to be able to just setup a spotting scope on my target and after pulling the trigger on my AR, I could just roll over and see the holes on paper since the spotting optic was already sighted on it.
I thought the need for using binoculars when going target shooting was unnecessary, but after taking a long range shooting course, I realized that the guy with the binoculars, even if they did not have a lot of magnification, usually high more visibility, a better field of view, and could identify movement faster than the guy with the high magnification on his rifle scope. The problem I still saw with some binoculars was that they were heavy and can easily reflect a lot of light. There are tacticals that can help you avoid portraying a lot of reflective light from your objective lenses, but the better option is to only use binoculars that get the job done, and not something that is an overkill. I’d recommend using binoculars that are atleast 25-30 mm as a minimum.