i think "unmounted" is just a regular photograph... no backing or anything on it like you were framing it. "mounted" photographs usually have a hard backing attached to it to keep it from wrinkling or curling in a frame.
i prefer mounting.
if given the option to mount or not mount... i mean, why would you not mount? and if you don't need alcohol to get it started.. .then shiz, i'd be mounting all over the place. west coast, east coast...