It is rarely used, it is used to form this tense: Futur II .
Formation:
For transitive verbs (having an object in the accusative) and reflexive (with sich , e.g. sich treffen ):
Partizip II + haben .
For intransitive verbs:
expressing movement or change of state, as well as the verbs sein, werden, bleiben :
Partizip II + sein .
For other intransitive verbs:
Partizip II + haben.