Is there an advantage of branching in version-controlled paper writing?
I use HG, but it is essentially the same as GIT, in that branching is easy. I branch all the time when working with coauthors. The branches tend to be short lived and merged pretty quickly. Basically, I distribute a copy to my coauthors and each set of comments I get back form different branches. This lets me see each authors comments individually. I then work on merging the comments back into the main trunk. Sometimes the merge is easy and the branch is one commit long. Other times it might take longer if I need to work out something (e.g., math, model, or analysis) which might require a couple of revisions before it is ready to go into the main trunk.