I recently [addressed this question][1] over at the Stackexchange Emacs site, but that post is more geared toward Emacs users. I'll say a couple of things here about general advantages/challenges of this platform for people who might be less familiar with it. As a sidenote, [my most recent novel][2] was written using Emacs.

DOWNSIDES

 - **Learning Curve** : Emacs has a steep learning curve, and most users do a lot of customization of the basic features over time. I'm not a programmer, but a literary person. I started with an unmodified "vanilla Emacs," and struggled. Emacs did not by default even wrap lines--each line just went straight on, right off the screen. If I was starting over today, I'd seriously consider installing one of the amped-up versions that community members create, such as [Emacs Prelude][3], that comes bundled with many commonly used packages. (Perhaps one day I'll make one of these for creative writers, but I'm not there yet.) Even so, Emacs will take time to learn. I didn't feel comfortable with it until I'd been using it heavily every day for about six months (and my general level of computer literacy was improved as a contingent benefit).

 - **Text Editing vs. Word Processing** : 
Emacs is a text editor, not a word processor, so it's missing some functionality writers might expect, such as pagination and headers and footers. When I have to communicate with a publisher about what I'm doing, I'll often export my work to `.odt` (Libreoffice) and then to `.doc` (Word), which is a little inconvenient, but I put up with it.

UPSIDES

 - 

**`org-mode`** : This is an Emacs mode for organizing lists, and it's the reason I tried Emacs out in the first place. It works beautifully    for large, complex manuscripts because it allows you to create heirarchies, all in plain text. Here's a screenshot of my environment:
       [![Emacs Screenshot][4]][4]

      These sections can be 'folded' and unfolded at will, and they can be    shuffled around at will, too, all with keyboard shortcuts.    Want to    switch chapter 2 and chapter 10? Easy. Want to see the    chapter titles    only, and not the content? Scenes? Only some    chapters and not others?    You can do that, too. `org-mode` also    supports the use of a keyword    called TODO, for things you're    working on. I use this to organize    things I need to remember. You    can also create COMMENT sections,    which won't be exported, when    you export.

 - **Text editing** Though it's somewhat of a disadvantage to miss out on the more design-oriented features of a word processor, I will say
   that a text editor is amazing at editing text. Every control is on
   the keyboard. I never touch a mouse or trackpad when I'm in Emacs,
   and there are also often multiple ways to achieve the same goal,
   which has been good for my arthritis. There's great search
   functionality, and abilities I'd never seen in a word processor, such
   as:
   
   `ALT-t` will transpose words. Put the cursor between the words "cats
   bats", hit `ALT-t` and you will have "bats cats".
   
   `ALT-k` will delete from your cursor to the end of a sentence.
   
   You can capitalize words with `ALT-c` or uppercase them with `ALT-u`.
   
   Emacs keeps track of everything you ever cut and paste during a
   session, and holds it in its `kill ring`. If you cut text1, and then
   text2, and then text3, and now want to paste text1, or text2, or text3, you can do it
   easily.
   
   There are many, many more conveniences along these lines.

 - **Git with Magit**
   
   I'd wanted to learn version control, specifically with [Git][5]. Git,
   like Emacs, is an amazing system that is used by programmers more
   than other kinds of writers. It also has a learning curve, but
   Emacs interfaces with it using a utility called [Magit][6], which is
   very convenient. I can log into [Bitbucket][7] (where I keep my
   files), upload versions, look at file histories, etc, all from within
   Emacs.

 - **To Sum**
   
   I've enjoyed using Emacs so far, but I still have a long way to go. I
   frequently hear about other ways of doing things, and    suspect that
   in five years I'll have different ideas about what    works and
   what doesn't. Nonetheless, I've been remarkably productive    with
   this software. Oh, and if you've ever been angered because    MSWord
   crashed on you, well, I have never seen Emacs crash yet    (YMMV...).

  [1]: https://emacs.stackexchange.com/questions/2171/what-options-are-there-for-writing-better-non-programming-text-in-emacs/14238#14238
  [2]: http://www.hmhco.com/shop/books/The-Trap/9780547824086
  [3]: http://batsov.com/prelude/
  [4]: https://i.sstatic.net/WFbrP.png
  [5]: https://git-scm.com/
  [6]: https://github.com/magit/magit
  [7]: http://www.bitbucket.org