islandora_book_batch_preprocess and islandora_batch_scan_preprocess have different means for outputting SetId.
islandora_book_batch_preprocess has a switch: --output_set_id, which simply outputs just the SetId integer after the command is ran.
islandora_batch_scan_preprocess does not have a switch, and by default outputs "SetId: integer"
Having different SetId output methods can be programmed around, but it surely would be nice to come to agreement and align the methods.
I don't have any experience with islandora_newspaper_batch. After reviewing islandora_newspaper_batch's drush functions, I don't see SetId output happening at all. Bringing the SetId output method to islandora_newspaper_batch would be highly desirable.
Outputting the SetId and subsequently utilzing it on islandora_batch_ingest, results in precision set ingest:
Precision set ingest can be leveraged to ensure only one set is ingested at a time in an orderly fashion. This strategy is mission critical for multi-employee digitization departments, where the possibility exists for multiple collections to be ready for ingest at the exact same time.