Posting comments is actually a demonstration of how the Advanced Security System can be used in some real-world situations. If your user role is set to
user (this is the default value when a new user successfully completes the registration process), you won't be available to post comments.
However, if the administrator changes your role to
Editor, or any other custom created role, you will be able to post comments.
Posting comments is just an example here, but you get the idea of what you can do by applying the same logic.