I believe @slm has provided the best answer. HOWEVER, there is another use-case. This alternative is a bit of a hack, though.
Rough guide. Do not consider these definitive commands:
- create an image file (ms-dos floppy or ISO-9660 CD)
- format the image with a filesystem, e.g. mkfs.msdos
- copy and manipulate files on image as needed, such as with mcopy, et al
- mount image on Guest VM cd-rom or floppy drive
It's not ideal, but it can work if your Guest VM won't allow network protocol connections between dom0 and Guest (such as during a closed VPN session).
More info here: