Suppose you’ve bought the best DVDR in the world and the best DVD recorder in the world and backed up all your precious work… but you’re about to format the hard disk… wouldn’t you give a try to Nero Speed or IsoBuster to check that every byte is healthy?.
Or the best recorder didn’t understand the best media’s chemistry, and chose a wrong recording strategy… better make sure!.
A scan may make you sure your new DVD-Video is Ok without having to watch all of it, that’s an invaluable help.
“If you do them every six months or so, you can check for any deterioration of the disc”. I agree, but would do so mainly to check for the recorder’s deterioration.