Remember that authentication happens when a user logs into your site, and enrollment happens when a user is made a student in a specific course. LDAP can be used for both authentication and/or enrollment. If you use LDAP for one, you do not need to use it for the other.

LDAP, external database, and IMS Enterprise File are all able to create new courses as they enroll students. All the other methods can only enroll students in the existing courses.