At one time, everybody not using Word or one of its evil offspring pretty much worked in and if you were an Emacs user it would be silly not to use AUCTeX. These days it’s easier to just write in Org mode and export to . For nontechnical documents that’s certainly easier but even for serious scientific writing you can probably get by with Org mode as John Kitchin has demonstrated more than once.
Still, sometimes it’s convenient to drop into and AUCTeX and for those times, Kazmierczak’s post is helpful. Get it set up and when you need it, it’s there.