You can back up virtual machines using the default subclient or create a new subclient to protect a specific subset of virtual machines.
When you create a virtualization client or a backup set, a default subclient is created automatically, and all virtual machines for the virtualization client are automatically included in the default subclient content. This setting ensures that all virtual machines will be included in backup operations.
To prevent duplicate backups of virtual machines, any virtual machines that are included in a user-defined subclient are automatically excluded from the default subclient. (Duplicate backups still occur if a virtual machine is included in multiple user-defined subclients.)
For an Azure Stack backup set, at least one subclient should be able to cover unprotected virtual machines. If you disable this feature for all subclients, some virtual machines may not be backed up.
When the default subclient is created, the Contents of subclient list in the Content tab displays All unprotected VMs as the content Type. That entry indicates that all virtual machines that are not included in any other subclient in the backup set will automatically be backed up by the default subclient.
To remove the default coverage, you can delete the All unprotected VMs entry.
If you remove all entries from the Contents of subclient list, All unprotected VMs appears in the list again.