For instance:
* A hook could gather info to know if a certain item/bib should be imported because of certain attributes (say, it wants to check something via XRECORD, or look at the holdings, or MARC, or time of day, and decide if it should be imported or not).
* A hook to do stuff on creation/update. For instance, let's say you want to auto-add stuff into a filefield, or make the node part of an Organic Group, etc. Maybe it could even say NOT to create/update the node...

Maybe both are the same, one drupal_alter()?