I've spent a lot of time borescoping .22 and centerfire pistol barrels. I have a lightly pitted 9mm P-09 barrel that would be tossed by someone with higher borescoping standards than mine, but it shoots lights out at 100 and 200 yards. It's just difficult to clean, other than that, it's still fine.
I have found that a borescope can be useful in seeing if one has successfully removed the carbon ring in .22 chambers however. To me, that is a good application of a borescope. I can see if I have the centerfire barrels clean but can't correlate the degree of cleanliness with the target results. What I know is that if I put one up with some carbon buildup in it and leave it for a few months, it might develop a little pitting under the carbon. If I get the barrel down to bare metal and put some oil on it and then put it in a heated safe, it won't corrode at all.
It's kind of fun to compare the machine work on an aftermarket barrel to a factory barrel using a borescope, but here again, I can't correlate a perfectly smooth bore with no chatter marks or scratches to an average CZ factory barrel as far as accuracy goes. But the finely machined barrel will be easier to clean, even if it isn't more "accurate".
I love my borescopes because they are fun to use. But I don't make many decisions based on what I see, mostly out of ignorance of the finer details, I suppose. So, fun yes, necessary no. And they can definitely drive some people crazy.
Joe