By default, Commvault creates an end-user role with substantial permissions which are not necessary for backup impersonation. So, we recommend you to create a new end-user role and assign the following permissions:
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Browse 
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End User Access 
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Data Protection/Management Operations 
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Job Management 
The end-users must be associated only with their backup set.
Note: Agent Management permission is required to edit the subclient properties. For more information on the available permissions and permitted actions, see User Administration and Security - Permissions and Permitted Actions.