Image and File: Why both?

I am new to Urbackup and was wondering, if the entire contents of a partition is backed up in an image, and if one can extract files from said images, why do file backups as well? What are the advantages of file backups on top of image backups?

My understanding would be if you did not want a full system backup due to the size of the system. Lets say all you wanted was a backup of the Users folder instead of the whole system you can specify file backup instead. Also, although i have not researched this yet, it would allow you to specify volumes/drives to backup instead of creating an image of all the drives.