It seems you are unfamiliar with the difference between RW and R type discs. :rolleyes:
DVD+R and DVD-R are write once discs. This means that you cannot overwrite any written content, however you can keep adding recordings until the disc is full. You can delete recordings, however just note that deleting one or more recordings will not free up space. In order to play these type of discs in any other player, you need to finalise them first. Finalising a disc writes the table of contents to the disc, however once the table of contents is written, you can no longer add any further content to the disc or making modifications to existing content (delete, rename, etc.). These discs cannot be erased either.
DVD-RW is a rewritable disc. When formatted with quick initialisation, it works in the same way as a DVD-R disc (append-only and must be finalised to play elsewhere), however you do have the ability to erase the disc.
DVD+RW is also a rewritable disc, however with this format you can overwrite content, delete content to free up space and play it in other players without finalisation. You can do the same with DVD-RW by formatting it with full initialisation first.
The main advantage with rewritable (RW) discs over write-once (R) discs is that rewritable discs can be erased or overwritten like VHS tapes, where as write-once discs become read-only once recorded, like CD-R's, printed paper, etc.