This particular tool is a must-have for serious Ubuntu/Debian administrators, because it allows the user to create a Live CD of the installed Ubuntu or Debian system More here

This has two handy uses: As a backup for your system or as a Live CD of your system. As a backup it will allow you to re-install a fully customized system in the same, simple manner in which you installed your base system. As a Live CD it allows you to easily install a custom system on multiple machines without having to go through the process of installing a base and then installing all of the applications you need to create your custom system.