The largest advantage to taking up the old floor and replacing the sub floor is that you get a chance to see if there are any underlying problems (i.e. rot, unevenness, cracks). When I had my floor tiles removed and replaced, it was found that the original sub floor was improperly installed, was rotted by the kitchen door, and was hiding some structural issues. Sounds scary I know, but I would rather find out about these things and fix them before laying a new floor than having to rip up said new floor later to fix them.