Wow those look like they are in great condition, the one may be new old stock (NOS).

Basically as stated above they are used to maintain a shave ready edge. The premiss is that at regular intervals you will do a few strokes on the hones to keep your edge in great shaving condition. In theory, if you did 4 to 6 passes once every week or two, or perhaps monthly, depending on your beard and shaving habits, you could maintain your razors edge indefinitely. That of course goes with the pretense that you are stropping every shave on linen and leather.