Normally you use a commandline tool called nib2cib for this which you had to execute everytime you changed your nib to get a corresponding updated cib. This arguably breaks the workflow a bit (it's pretty easy to forget to do a nib2cib after modifying your nib). The tool Klaas Pieter created aims to eliminate that extra step by watching your resources directory for changed nibs if I've understood correctly. Once it detects a changed nib it will run nib2cib for you on that nib for a fresh cib.
Thanks for the link.