The revision functionality in XperienCentral is not enabled by default. See XperienCentral Revision Settings for complete information on configuring the settings for the revision functionality.
When the revision functionality is enabled, saving content items takes longer than it does when the revision functionality is disabled.
When the revisions functionality is disabled, XperienCentral nevertheless keeps track of revision numbers. For example, if you create and revise a content item 6 times and then turn on the revisions functionality and save the content item 2 more times, you will see in the Revisions tab revision 7 and 8, which can now be reverted to.