The first overview of a document is often presented by a table of contents. However a screen reader may have difficulty inferring a usable reading. With an untagged document it relies on the screen reader inferring the structure, to pass to the underlying Accessibility tools.
On this document foxit produces the following reading (Acrobat is similar).
Using the tagged PDF, the structure is made explicit to the screen reader and typesetting artifacts such as leader dots are marked as artifacts and not read, producing a far more understandable reading.