In Sitecore, whenever there is a need to create a new site, we just add site definition through configuration. In this we have the flexibility to order the Sites by changing the order of site definitions in the configuration.
In SXA, sites are defined as site items instead of configuration (although we can still use configs). We can manage all the Sites using Site Manager.
But imagine, we changed the order of sites (for resolving purpose) using Site Manager and want to move this change to higher environment. We need to serialize or package the item to deploy. But where are these changes get saved?
You can find the main Site Manager item: /sitecore/system/Settings/Foundation/Experience Accelerator/Multisite/Management/Sites