Just to be the devils advocate, Ive spotted for a friend out to 900m +/-10m, close to a grand; with 10x binos in the sitting position using the inside of my knees as support. I was able to make accurate wind calls, see impacts and vapor, which I was able to see vapor through the entire FOV, unlike only being able to see it after its max ord. (last 1/3 to 1/4 of its trajectory) in most spotters Ive used. And you get less eye fatigue after long periods of observing, whether its from trying to keep one eye closed to look through a spotting scope, or seeing 2 different images, one non magnified and the other magnified.
That being said, 10x or 12x binos are pretty limited to what they can do, some dont have the capability to mount to a tripod unless you use a rest or a HOG Saddle to clamp it, youre unable to zoom in to see actual precise impacts on steel (most binos at least, unless you get variable power binos, I have never used them), and you can barely see impacts at 200-300 on paper.
Image stabilizing binos are awesome for spotting, even more so with a tripod as it wont pick up the small, but visual vibrations from the wind. Unfortunately theyre quite expensive.
Trying to spot impacts for short periods of time, or observe mirage right before you shoot, Id rather have a spotting scope, spotting for a group of people on steel targets for longer periods of time, Id rather have binos in the 12 to 20 magnification range.
Also, food for thought, it can be more difficult to get on target or find the object youre going to observe with an angled spotting scope versus straight spotting scope scope or binos.
