Dragon Burn gives you the option of writing the contents of an audio, data, mixed-mode or CD Extra CD as a disc image file. A disc image file is a single (usually large) file created on your Macintosh that represents the entire contents of a CD.
The advantage to creating a disc image file is that the it can be used to create subsequent disc copies without the source CD. This is particularly useful if you will be making multiple copies of a CD, and may not have access to the original source CD.