Backing up files to CD-RW or DVD-RW might be cheaper than buying a decent sized flash drive or splashing out the equivalent of about ??10 per 100 GB on an external hard drive - but keeping track of precisely what is stored on each optical disk can be an absolute nightmare - particularly if any individual folder you wish to backup is larger than 4.7GB. And storing multiple optical discs takes up sooooooo much more space than just having one slim 500GB + external drive! Optical discs can also get scratched quite easily, making it difficult if not impossible to retrieve your data from them.
And whilst Windows Live File Format may allow you to "incrementally add files to the discs", unless you leave plenty of room for expansion from the outset, you will probably have to keep starting again from scratch or you will end up with document files squeezed onto a disc that has mostly pictures or software downloads etc!
With all the drawbacks that optical discs have, I would never recommend anyone using them unless they really cannot afford a portable hard drive or a decent sized flash drive.
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