Hi again Mark,
LDAP is traditionally used to synchronize user accounts across multiple applications. So, it can be used to ensure that user accounts are consistent (and one account can log in on different applications) on your OJS and OCS installation, or even on a Drupal, WordPress, or other application. The complexity of setting up LDAP is what prevents us from making it the default authentication service (and that most people don't use it). Also, it is looking more and more that we are going towards the use of Shibboleth (http://drupal.org/project/shib_auth
, located in the plugins/implictAuth/shibboleth folder) for user authentication, which is more powerful than LDAP for several reasons, esp. single sign-on (e.g. signing in to one application automatically signs you in to all others).
Hope that clears things up a bit,