The Restore System procedure is performed when the complete instance has to be restored or moved to another server, but there can be a scenario when you just need to restore a single project from another JIRA instance.
Let's take an example of a company that has multiple JIRA instances used by various other business units. These business units work independently of each other; they have different teams and work from different geographic locations. As you know, these days companies do reorganization quite often. Due to this reorganization process, a few projects from one business unit need to be transferred to another business unit. All the project code and documents along with the projects need to be transferred as well.
In this case, we cannot simply take a backup of one instance and restore it in another because it will wipe out the data in the target instance. The restore process has to be done only for a few selected projects.
Atlassian understood this scenario...