Overleaf allows you to work with several authors at the same time on the document. I was skeptical (after all, git allows that too). But after using that feature, well, it is just the killer thing. Now Overleaf doesn't add much on top on my own Latex installation. But the collaborative thing is just spot on (much like Google docs which I have discovered not a long time ago; same analysis : not that good presentation tool, but working together is just incredibly useful).
In my experience, Overleaf is actually awful for collaboration. Maybe my workflow is weird, but I tend to look at the diffs after my colleagues make changes. Also, we mainly use pull requests to add to our papers. This way, everyone can see and comment on changes.
This kind of workflow is not really usable with Overleaf. Overleaf uses Git in the background, but every commit is named "changes on Overleaf" and the individual commits do not really make much sense. In addition, everything is immediately put into the master branch and there's no way to summarize or group changes (like with commits and/or pull requests).
My next problem is, that Overleaf just uses latexmk so if you have some code to generate graphics or tables, you have to compile and add them manually all the time.
my workflow is different : we use voice chat to share and we edit collaboratively. Both these allow to actually work together and, more importantly, think together.
That's very interesting. I honestly didn't think of that, since we often worked asynchronously or at the same machine (which doesn't work at the moment, of course). I can see how Overleaf can be nice for that purpose.