How does the overwrite file option work when using a rewritable DVD?

When using a DVD+-RW as your backup media, you can select "append" or "overwrite" the content. Start you backup project, click on "Options" => "Disc":
Select "Append the backup file to the disc" to append the new file on the multi-session disc.
Select "Overwrite the data ton the disc" to erase the whole disc and write the new file on the disc.