Last tested: Sep 18, 2020
These are created the first time a user enters dev mode.
IMPORTANT NOTE: Entering dev mode will create copies of all project files, regardless of what they're switching modes from. i.e. if you're switching to dev mode for the first time from the Browse page, you'll still generate files for all of the projects.
This means that the initial mode-switching process could take quite a while if you've got a ton of LookML files on your instance, even if they're in multiple projects and you're not accessing a project (via the IDE).