wow never used a rewrightable, i mean rewriteable DVD before.
Yes you can store data on them but pay attention to the + or - signs on your DVD writer. Now-a-days they all come "+-DL" and buy the appropriate blank disc.
Re-writing you must only add to it, as long as it isn't finalized. And if your rewriting it must be larger then the data already on the disc. You can't rewrite a disc with 400mb already on it, with 399mb worth of data. As you must use those sectors already used.
And its all about preferrence, as if you have data you dont want to loose you will put it on a DVD Disc unlike a flash drive which is for mostly tempory storage.. the USB disc can be corrupted, formated or plain fail... DVD rewrite disc will never be replaced, just as Tape media which is now the best form of data backup and so is the DVD Disc, and BlueRay Disc will make lovely backups too.