It may be helpful to think of it as the “Overview Drawer” rather than the “Documents Panel”. There isn’t much documentation talking about it, but in a few places this is indeed what it’s called. So you’re getting an overview of your documents, and that does include the parents within them.
This drawer isn’t just for document-management; it also provides a way to navigate your entire collection of Databases more quickly. It can serve as a kind of “Table of Contents” if you leave it open while working in a large Document, although it ‘forgets’ the scroll position after you switch Boards so it’s not quite perfect in that way.
Note the commands for expanding/collapsing all selected/unselected Documents under the “…” button, this may help you keep your Drawer tidier-looking.
