A common problem with packages comes about from the fact that frequently the contents of the package needs to be "localized". Configuration files and scripts need to be modified after the package is deployed to taylor the package to the system it is deployed on. The problem is that these modifications are erased every time a package is upgraded. There are many solutions to this. What GPT does is allow the configuration files and scripts to be put into a special package called a "Setup Package". GPT then enables the relationship between this package and the original package to be expressed with a Setup Dependency.