In a Journal Transformation migration you might want to migrate active user content into inactive alternate mailboxes. This may simplify the migration and reduce project complexity. You may also want to do this if active users recently departed the organization or re-join after leaving.
In the Bulk Mapping wizard, when you select the Journal Transformation options there is an option called ‘Use alternate mailboxes’:
If the option is enabled all collected Journal Transformation users will be treated as leavers after consolidation. This means that the users will be managed from the Journal Transformation Leavers Management page in the user interface.