[jordanlev]

It's an easy distinction: if non-programmers are managing the content of the site, don't use a static site or a static site generator.

Asking people whose job isn't "building websites" to edit text files, run some sort of compiler on the command line, connect to a server via FTP, or deal with version control is a total failure mode.

But if a developer (or an especially adventurous designer) is going to be editing the content of the site as time goes on, then static files or a static site generator can be a great option.