The Resource Manager Portlet allows you to publish pages developed on one server to another (You can also publish page from one virtual portal to another in same portal server). After publishing the page would be initially visible to only limited set of users (By default to administrators but you can change publishRule, personalization rule to add or remove users) and once you review page on the target server you can promote that page so that it becomes available to all the users.
After promoting a page to all the users you can demote it so that it is no longer visible, in that case portal will check if there is a backup of the page if yes then backup page becomes visible. Portal maintains backup of only one last page.
Please note couple of important limitations on Site Management
1) You can only publish a page which has unique name. It looks like the Resource Manager portlet is using unique name to relate page on source and target. The Resource portlet adds published word to the unique name while publishing it on target
2) Source and target portal should have parent page with same unique name for the site management to work
3) You cannot mix Site Management with xmlaccess. If your using Site management for publishing you will have to stick with it, trying to use some other method would break it. It must because of the logic in Resource Portlet that relates source page to
Read Portal Transfer using Site Management page for more details on the