Admins, PDA/Loans: The difference between a PDA profile's "Search criteria" and its "Collection"

Each PDA profile has two parts:The typical approach to setting up a PDA profile is:
  1. Set up the search criteria
  2. Run the search
  3. Add all the titles returned by the search to the collection
  4. Make that collection of titles active and available for your patrons to use
The search criteria and the collection are in some ways separate and distinct:The key to understanding PDA is recognizing that the search criteria and the collection are separate.  The search criteria can be used to add titles to the collection, but not to take titles out of the collection.  And the collection can be modified directly by either adding or removing titles - regardless of whether they match your search criteria.