The Documents section records text or abstract text of any census listings, deeds, wills, or other documents. Each document is maintained as a separate entity to minimize the chances of its text being compromised with commentary or editing, and to enable the same document to be linked to multiple records (such as beneficiaries or witnesses in a will, or multiple families in one census household).
Also, sometimes document information will come from a source that you have (a personal book, something at a library, or a paid online resource) that other researchers will not have. So in recording it here, others have the full source information they would not have had otherwise.
An additional benefit is enabling the ability to search for people who do not have a census found, in the People Without Census report.
Clicking the type link goes to the editing page if you are the document's moderator; otherwise it opens up a view page for the document.
Clicking a name linked in the document text goes to that person's individual page.
Each document also appears on a person's Timeline page.