For testing various setups I feel it more comfortable to use tar
archives instead of images.

 - You only save programs and data, no need to fiddle with nullbytes to optimize compression or shrink partition sizes.
 - The size of the sd card doesn't matter. It is easy to get the tar ball from a 16GB card and extract it onto a 8GB card (when the programs fit to it).
 - You are more flexible in creating additional partitions.

**Is it possible to use tar balls instead of images to backup Raspbian?**