What circumstances would this be useful? A common example of this being used would be for an manager and their assistant.  If these two employees are added to an absence rule to not be away together but the manager is added to the exclusion list, the software will not allow the assistant to be away when the manager is away, but would allow the manager away if their assistant is away.

The rule is highlighted as exluded in the leave request and in My details > Leave (dropdown menu) > Applicable rules.