Background: I’m a technical writer, and everything I write is under version control. Currently mostly Perforce (P4), but also git/GitHub.
Advice: Unless you have a specific, concrete, well-defined reason for using git/GitHub for managing your writing, you should avoid it.
Ignore if: You’re a developer (or other person) who’s been using git for a long while, and have absolute confidence in your skills and workflows of using it.
Why: Git and GitHub are going to introduce complexity and friction into your writing workflow. Even the difference between two version control systems (P4 and GH) can be enough to trip you up. (I’ve seen it happen to dozens of writers at this point.)
I’ve been using git and GitHub for 10+ years, for other things, and I hate using it for writing. Not because I don’t understand it, but because I spend too much time managing PRs and other engineer-oriented workflows. (Managing edits/feedback is especially frustrating, for reasons explained by others in this thread.) This is time that I lose my focus on the writing part of my job, the part I like most, and that’s frustrating.
If you really need version control, especially if it’s for collaborating with others, then GitHub can do the job, and you can learn to use it. Don’t let me scare you!
But unless that’s the case, adding GitHub or git to your writing process sounds more like procrastination on your writing than something to seriously consider. 