taken from http://www.jayfisher.com/Blades.htm#CPM154CM
excerpts for this portion...
"If you need a very good technical reason for a mirror finish, even in a utility working knife, it's corrosion resistance. All steels benefit from a reduced surface area that is the result of mirror finishing. When a blade is ground or sanded to finer and finer grits, the surface scratches become smaller and smaller, and more and more shallow with each diminishing grit size. The surface of the metal is like a field of furrows, starting out deep and rough, with the surface broken up in hills and valleys, grain exposed like dirt clods in freshly plowed land. You can visualize that a tremendous amount of surface area and roughness is exposed, and the more surface area, the more contact corrosive fluids and oxygen will have with the components in the molecular crystalline structure of the steel. This is like the plowed field's ability to take on water. Now, as the field of steel is finished finer and finer, these rough surfaces, hills, and valleys are reduced considerably. So, then, is the surface area, and more corrosion resistance is obtained. But when brought to the finest mirror finish, something entirely different happens. The act of polishing literally melts the microscopic surface of the steel and blends the smallest furrows and imperfections into one monolithic surface. It's like spreading a layer of clay onto our smoothed dirt field, thus preventing water from penetrating, as it is trapped on the surface. Since the surface area is reduced to a minimum and smoothed, the steel (and every other metal polished this way) is much more resistant to corrosion. Since corrosion is a reaction of oxygen and often a fluid, minimizing the surface area assures the greatest corrosion resistance. The surface, like the surface of our clay field is slick, resistant, and clean. Not so great for the farmer, fantastic for steel and its corrosion resistance."
"A Mirror Finish is best, for a host of reasons. It's beautiful. High chromium and alloy tool steels can be made to obtain a gorgeous finish, even D2 with its characteristic orange peel appearance is enhanced by mirror finishing. A mirror finished blued blade is stunning. The mirror finish has the highest appeal among most collectors and users. It increases the value of the knife, also the cost as the blade labor is more than doubled (that's probably why most makers just sand their blades). Historically, the mirror finish is found on only the highest valued jewelry, firearms, blades, swords, and armament. A mirror finish doesn't hold debris, water, or corrosives. The blade slides through materials with less effort. And there are some studies that indicate a high polish increases the break resistance of the blade, because all fractures start from a surface imperfection."