[Woodnotes Guide to Emacs for Writers], written by Randall Wood in 2005, describes the benefits of using Emacs for writing prose rather than program source code. (PDF)
An extensive list of Emacs resources is at the [Emacros] SourceForge page.
For learners, an excellent introduction appears in [Learning GNU Emacs, 3rd Edition], by Deborah Cameron, Eric S. Raymond, and friends (O'Reilly, 2004).