If a library wants to not allow on-shelf holds (if all unavailable), item groups will not be feasible for them, and short of creating a separate item type for multivolume records, setting on-shelf holds to 'if any unavailable' is probably not specific enough either for the combination of item eligibility that might arise. And academic/special libraries are both likelier than other libraries to disallow on-shelf holds AND benefit from item groups and their associated holds. To confirm: Enable item groups and item group holds; have a record with a couple volumes/item groups set up. Have a circ rule for that item type with on-shelf hold policy of 'only if all unavailable.' Check out a volume in an item group to a random patron, ensuring that no items within that group are available. As a different patron, from the OPAC, try to place a hold on the volume with the checked-out copy. See that the hold is blocked with 'There are no items that can be placed on hold' message.