This numeric value records the depth in the UCS org-hierarchy at which the policy governing the external destination binding attached to a scheduled backup/export policy is actually defined. On a BackupExportExtPolicy object it tells you whether this particular instance is inheriting its settings from a policy defined at the root organization or from one defined further down in a sub-organization closer to where the job or policy is scoped. A value of 0 means the controlling policy lives at the top-level root org, while a value like 2 would mean it was defined two levels down in a nested sub-organization.