UpdateXpress System Pack Installer is designed to download and apply UpdateXpress System Packs. The System Pack is a collection of individual updates as specified by the UpdateXpress System Pack XML.
When running the Installer tool from the CLI, the tool downloads and applies System Packs by default. If you want to work with individual updates, specify the -L (--latest) argument.
When running the Installer tool from the GUI, you can select either UpdateXpress System Packs or Individual Updates. In most cases it is recommended to work with UpdateXpress System Packs, but the option to also work with individual updates gives you the greater flexibility in choosing which updates to use.