I'll come in and say that Overleaf has been invaluable when you're working in teams and need real-time editing and/or your team members don't know how to/refuse to use Git (cough some academic settings cough)
I prefer git for the bulk of the writing process because it lets you make well structured commits, use your favorite editor, and doesn't depend on having a strong internet connection.
Even so, you can't beat overleaf for the final stages of paper submission when all the authors are making tiny typo fixes and style edits in all parts of the document concurrently.
