Well, as I see jigdo gives you big advantages on the server side. On Debian you can assemble the files with a packages mirror, too, and don't need to keep the isos everywhere (see jigdo website). This brings much more mirrors in the field, but Sabayon has no packages (yet) and therefore no package mirrors.
Where are the advantages on the client side?
Torrent has the big advantage of sharing your upload, too. You can even buy a DVD and support Sabayon