An image file is beneficial as the storage media is not required for recovering the data and that the data can be recovered at a later stage using just the image file.
For example, when you have a hard disk, which has bad sectors in it, or when one is not sure that a hard disk may work properly the next time, it is advisable to create an image and then recover the data from the image itself and not the crashed hard disk.
Stellar Mac Data Recovery software creates a sector-by-sector image of the selected media. User can also select range of the selected media to create an image. Later on, the software uses the image to recover the data.