Disclaimer: I don't know the details of how this works.

Time-to-solution and quality would be my guess. In my experience, adding high level important details about the way information is organized to the beginning of the context and then explaining the tools to further explore schema or access data produces much more consistent results rather than each inference having to query the system and build its own world view before trying to figure out how to answer your query and then doing it.

It's a bit like giving you a book or giving you that book without the table of contents and no index, but you you can do basic text search over the whole thing.