I'm currently working on my thesis (alone) which I also sync between devices using github. I work on it locally in VSCode and wrote a small makefile to compile/clean up/etc.
I get the appeal of overleaf for collaborating (I never used it myself, but it seems like a great platform!), but what is it that you consider a massive improvement in overleaf over git+local compiling?
you might like latexmk, which automates running the right tools in the right order. It's pretty neat. It detects whether to run bibtex or biber (and when) and whether another run of (pdf|lua|xe)latex is required to resolve references/citations/..., etc.
You were right, I did like latexmk! Thank you so much, this will definitely make live easier for me in the future. I don't know why I didn't know about this sooner.
Fundamentally, because of "reduction of steps" [1], although the workflows might be otherwise functionally equivalent:
(1) The cognitive overload of the git push and pull - while this might have seemed small when I was using this workflow, I don't have these steps anymore making them seem unnecessary in retrospect. Reduced steps in general are better IMHO: same reason as to why I might use something like Google docs, even though, a somewhat equivalent workflow would involve going via GitHub.
(2) Ensuring all local environments are similar or identical. Esp. a problem when installing new packages, say on device 1... when compiling on device 2, I need to either remember to do this by noting it somewhere (e.g. modifying the makefile), or I am reminded of it with a compilation failure.
Small gains perhaps, but they add up. Esp. if you are working on multiple documents at the same time (I typically have 2-3 active documents).
[1] If it matters, I need to switch between 3 devices running windows, ubuntu, elementary OS.
I wrote my thesis with git + vim + latex. The main issue with collaborating like that is that you require other people to be able to use, say, git + vim + latex.† That may not be a problem for you and your colleagues. If it is however, Overleaf basically reduces it to "please open a web browser and have a look".
The other major argument is, of course, that you get an off-site backup "for free" for something as life-changing as your doctoral thesis, too.
†Of course, the other thing about having lots of local commits is that you can easily graph, say, words as quantified by texcount vs time and include the resulting diagram in the final copy of the document...
You're answering a different question from the one that the GP asked. What's the advantage of using overleaf over git + $EDITOR for a document with one author? Regarding off-site backups, that is already provided by your git host (github/gitlab/...)
I get the appeal of overleaf for collaborating (I never used it myself, but it seems like a great platform!), but what is it that you consider a massive improvement in overleaf over git+local compiling?