This, the dependencies are annoying to deal with. With ShareLatex, it "just works"
Re:ShareLaTeX Joins Overleaf
by Tijdreiziger on Thursday July 20, 2017 @04:10PM
(#14815854)
A local MiKTeX installation handles this beautifully (MiKTeX is a LaTeX distribution which comes with a bare set of default packages, and then downloads packages from the internet transparently upon compilation if they're necessary).
It's significantly easier to do collaborative editing of latex files with such a web service. But even a single person might want to use them, because maintaining latex dependencies can be bothersome.