When you discard a draft billing document, the related billing document line items are deleted. In addition, the related billing schedules are deleted or the Billing Document Line Item field is cleared on related billing schedules. The action taken depends on the Delete Discarded Billing Doc Schedule field in the Billing Central custom setting. See Delete Discarded Billing Doc Schedule.
To discard a single billing document from the Billing Document Detail page:
To discard several billing documents in one go: