To what problem is distributed information retrieval the solution?

Distributed information retrieval (DIR), where a single broker coordinates retrieval from many independent search services, has been extensively studied but typically without any particular application and sometimes even without any explicit motivation. There have been a handful of arguments given for DIR—coverage, effectiveness, and ease of use, for example—but these are not borne out by experience. Are there uses for DIR? There are, but generally for organizational not technical reasons, and they have not been well studied.