The Directory gives the users a complete overview of all the channels and/or courses, they have access to.
You can decide whether the directory should public or private. If you decide upon a public directory, you will be able to make public courses available e.g., for customers to take. This can be done anonymously without having to register, but with the option to register to achieve a badge for the course finished.
With a public directory, you can still have private channels and private courses which only are available for e.g., partners or employees.
If you know you are not going to need to make public courses and want to keep everything private, you just pick the option for a private directory.