No, you're duplicating your output there

. The ISO image is essentially a file that contains all the info to burn a disc directly - in Nero for example, you can just burn an image with a few clicks. So rather than drag and drop the files created by "DVD" (Vobs etc) into a new DVD, you just burn the ISO.
The ISO is a neater way of packaging your files. If you ever need to get at the files in the image, just unpack with ISObuster.