If it's just files i.e documents you are backing up you are better off using a re-writable disk. That way you can re-use the disk and replace the updated files. You could use a CD-R using packet writing/multi-session, but once it's full that's it. If you are backing up a complete hard drive, system, files, data etc, you will still be better off using CDRW, as it could take between say 2-7 disks, if you can afford to throw away up to 7 cdr's a week then use CD-R's.