Is it a good idea to use online editors?
You did not mention it in your question, so I think it is important to tell it.
Disadvantages:
- Data Security. Are you sure that only you and your guests can read the document you are writing? Is it not possible to reach your document by guessing the web adress? What's about the computing center where your datas are stored. What if you are writing a scientific work, that should not be published by someone else. A remark: Some students in germany are not allowed to use programs in clouds for writing bachelor or master works. That depends on the company they joined for bachelor or master work.
- Suppose the web page is down or the service has been shut down. What's about your documents? Have you backup's of them? To run them now you need an installed TeX distribution.
- Are you sure that you can use all packages you need for your work? Are you sure the packages are up-to-date? Are you able to use an local texmf if you have to use an older version of an package?
- At last you have not the control over the compiling process you would have using an installed TeX distribution. And then you have also the control to update or not update your distribution. Suppose a soon deadline for your work, and an update causes problems with comiling.
- Templates can help, but must not. Templates are only helpful, if the user understands what the template does. That is usually not true. Therefore the user runs into problems caused by an template that she/he did not understand. So better start without templates ...
- you're tied to a commercial service and their terms of service. What if, all of a sudden, they charge you for that service? Or insert advertisements in your documents? Or claim property of your content? Or just close? You're bounded to any change in the terms of service, and if you don't know how to migrate the data you saved on their server, or if they make it complicated to save them, then you might lost a lot. (Thanks @Clément for his comment!)
Advantage
- You need not to install a TeX distribution, but you have to use that thing that is provided by the online editor and the used TeX distribution.
- prepared templates can be helpful, if one checks the code an do only use the parts one does understand.
For me the disadvantage of data security is the reason not to use online editors, but that is---of course---my personal opinion.
In addition to all the good arguments in https://tex.stackexchange.com/a/301974/36296, and leaving the TeX level, running your code with a local distribution has the advantage that you can use whatever editor you want. Some offer pretty convenient features, just a few examples from the top of my head:
Shortcuts and even custom shortcuts: Often using the same worklflow? Assigning it to a shortcut can save a lot of time.
An editor you already use: Use one program you already know from other tasks like programming.
Code snippets: Use the same code building blocks again and again? Code snippets can make it easier to find them.
Buttons/menus/displays etc.: Many editors provide plenty of features to help writing tex code. Menus to select font sizes, hierarchical structures like
sections, various kinds of letters and symbols - Graphical assistants to insert figures or edit tables - autocomplete commands, words or labels and cites - display tooltips about commands ......
Of course they are not available in every editor, but remember, working locally you have the freedom to choose whatever you want. For a list of available editors, including their main features, see, e.g., LaTeX Editors/IDEs
Besides these considerations about the editor, on your own system you can use all the cool Tools for automating document compilation whereas overleaf only uses latexmk (as far as I know).