It can be very handy to rip discs to an ISO file and have a good virtual drive program as well. If you are in the habit of testing your media, you can use an ISO with CdSpeed/Discspeed or Opti Drive Control to burn a test disc using something you need to burn to disc rather than the standard random data disc they would create otherwise.
Unfortunately, Windows and many playback software can't access the files in the ISO. The virtual drive program takes the iso file and makes it appear to Windows or any other program as a disc in a DVD/BD drive, giving full access to it's contents as if it were a physical DVD/BD drive. Easily used by video playback software or video conversion software. I use Virtual Clonedrive myself.