In a lot of environments it is harder to use external files, because deployment of these files to the appropriate location on a webserver requires special privileges that not everybody has. In those cases storing these files as Static Application Files or Static Workspace Files might be a better solution.
When you install the browser extension, a little Select List appears in the page where you can see your Static Application (or Workspace) Files. You can just select one of your files there and a built-in editor appears with all the nice Visual Studio Code features we all know and love.
So you have syntax highlighting and can edit multiple files at the same time in different tabs - either behind each other or next to each other (left to right or top to bottom).
And it's not just that you van Edit and Save the file, there is also a "Minify" option. So you can even do that directly from with APEX! That is really cool.
And to top that all off, you can also create (or edit) Less files and compile these to CSS (and minify them) in one go.
So no more excuses for not using files anymore! It will never get easier than this ....