The WEM Live Runtime is the Production Environment for your application. In the Publish feature you can activate both Staging and Live in one go. All settings and features in the Modeler are published first to Staging and updated in Staging Environment, and then to Live and updated in the Live Environment. Publishing is needed when changes are made in the Modeler that need to be implemented in Live Runtime. You want to publish only the finished and tested updates to this environment to make sure you keep a working application exposed to your users.