Although it's mighty inefficient to have multiple files on the same server, it is sometimes necessary (SSL vs. standard site with images...depending on how it's done) and sometimes I just have a file that I need to tweak only a TINY bit but will appear extremely different (due to templating). Either way, having a copy method would be very useful.
...like when I use my "temp" or "test" directories to try out new options, I can copy/paste stable versions and keep tweaking the original, rather than having it completely moved.