Mirror polishing is a carry over from days when steel implements rusted because they got used daily. A high polish leaves less open area in the finish for moisture and rust to set in. Modern steels, and the average amount of use most knives get, make this less of a thing. It is also a very good way to determine the quality of the work your maker is capable of. There are a lot of guys making knives who just can't do a mirror polish. And there are some who probably could, but won't, because a mirror polish shows imperfection like nothing else.
Matte, bead blasted, or Scotchbrite rubbed blades are a heck of a lot easier to produce, and therefore cost less. Time is money, and if the mark is willing to accept what would have been considered substandard work 100 years ago, well that's what they provide.
One of my "go to" patterns to check a makers grinds is the Loveless New York Special, a smaller fixed blade that, properly done, has deep concave grinds with edges on both sides of the blade. A guy really has to know his stuff to get that right.
sometimes the sharper and cleaner angles and edges are rounded out in the polishing.
This is a sign of poor craftsmanship.
Let me give you an example that's not knife related. Take a look at a Colt, S&W, Merwin Hulbert, or any other top end firearm from the late 1800's, or even one built up to around the 1930's. If it's in like new shape the lines are perfect. The bluing (done by hand in a rust shed) is deep and mirror reflective. That blue (or nickle) was applied to a mirror polished piece of steel. And rubbed out multiple times before the final polish. And the lines are still true. That's craftsmanship, and there's damn few who can still do it.
Traditional Japanese blades are mirror polished, not for looks, but because it makes a better blade. And if you're using a blade hard than a fighting samurai (and scratching the heck out of it) you're doing it wrong.
