When she is unsure about a re-structuring of part of the thesis she makes a branch. It happened twice so far.

Same reasoning for branching when your are single author of a repo. containing code, I guess. A major refactor or structural code change or trying sth. "crazy".

My partner wrote her Social Science dissertation in LaTeX and also used branches. They are particularly helpful when you hand out a version to others for feedback or proof reading while still working on the document yourself.