So on a OES (Used to be I would say Netware, but now it can run on SLES with OES as well) server with millions of documents, and hundreds or thousands of users, you can enable Quickfinder, and index all the files. (Including content inside Word, Wordperfect, and PDF files).
Then you can make the index available to search.
An anonymous user can search and see basically nothing, or maybe the contents of sys:\login (whatever [Public] trustee has access too).
Then I login as user Jsmith. I can find files in Jsmith's home directory, files in shared folder he has access to and so on.
Logout, login in as BWilliams, now I do the exact same search, and I see different results, since I now can only see the contents of the BWilliams home directory, and the shared folders he has file system access to!
Lovely! This means with one index, you can generate custom search results per user!
Not many other search engines can do this. The requirement is that the files be stored on an NSS volume on a server in the tree for trustee based searches to work.