The usefulness of a magnified view is generally only apparent to those who have had the opportunity to use one. People who have not used a stereo microscope can be forgiven then, for not understanding the benefits that follow.
Stereo microscopes are not very high power, my old beat-up Swift for example offers 20 and 40 power. - But it is truly amazing what that bit of magnification can show you, that you never might have suspected the existence of before.
I use it most often to examine once-fired cartridge cases. When you hold the case in your hand, it's just smooth brass and not particularly interesting... Under magnification, you discover that it is not so smooth and homogeneous after all. There are stress cracks, manufacturing flaws and places where the brass has flowed into imperfections in your chamber. All of these tell you things about your brass, your load and your rifle that cannot be discovered by looking at a piece of brass in your hand - no matter how hard you might squint at it.
The stereo microscope is another tool like the video bore-scope, it takes you to a higher level of awareness, and teaches you things about a firearm, in areas where the naked eye will leave you in ignorance.
So - I do not have to wait for a case separation to discover that I am pushing the shoulder too far back for a particular gun's chamber. Early on, before the brass has been significantly damaged, I will see the stress cracking near the base that is normally invisible, and adjust my die with a feeler gauge when loading for that rifle, so that the shoulder moves up a few thousandths. - Or in an extreme case, adjust the rifle's headspace.
I have been able to see things like this for years - but now I can make images of the damage and show it to a customer who formerly just had to take my word for it that his firearm has headspace issues. I am excited about being able to offer this service, as few other gunsmiths do - and it really is better to address problems like that BEFORE a case separation or other unsafe incident ruins somebody's hunt, looks or eyesight.
Then there firing pin tips, extractor claws, various small mechanisms and any tool which must be sharpened to consider.
Why more gun enthusiasts and gunsmiths do not use these devices is a mystery to me. - I just looked at 'used stereo microscopes' on E-Bay and found dozens on them that look a lot better than my old war-horse for under 100 bucks, some for less than 50.
My old Swift war-horse, with advanced Black and Decker penlight lighting system:
Random piece of .223 brass:
End Mill - Nice and sharp!:
Hex Key showing wear:
I thought my pocket-knife was sharp:
Dead House-fly, attacked by fungus:
The main thing is to learn stuff and have fun.