This option only applies for official sites.
In case you want to test your site before changes are applied to it, you need to enable this feature. When we update Drupal core and/or modules, site admins with stages updates enabled will receive an email regarding the creation of a sitename-preprod.web.cern.ch site.
This site would be a clone of the production site but with all the updates applied. The site can now be tested during 10 days to see if any of the updates is affecting the site. After this period the same changes will be applied to the production site.
Please remember that any changes on these preprod sites won't have any persistence, as they are only intended as testing sites.