Documents is a place to gather documents and files where you can write a brief description of the file you uploaded. Can be used, for example, when you work out a log and discuss different ideas.
The advantage of Documents is that you can write an explanatory comment on the file.
Files is a file archive with version management.
The advantage of Files is that you get access to all versions of a file that have been prepared, and can see how often the file has been downloaded.