Look at your workflow needs, your purpose, and your out put
do you need to be able to back up 4.7 GIGs of information
if your work is in video, i personally like to have a copy on optical storage, after i slice all my fottage and have all clips arranged and different files, i like to have that as a back up just in case the hard drive crashes, or i do something stupid
again if your working in video, out putting to DVD as a final copy is great, lots of clients jumb on that option now
but if you never plan on doing any video work, and you can't see your self needing to back up 4.7 gigs of information at one time
then a combo drive is more then adiquette