This is a desperately needed feature as it serves a more common use case than either of the current options (email verification only OR manual accounts). In fact, email verification -> admin approval is probably the most common account creation method for closed communities (doubly so for online courses). Having the email verification first means admins have fewer spammers to deal with. And the current email-verification-only option is clearly inadequate if even the official documentation warns users not to use it due to the large amount of spam it will incur.
The email self-signup + admin approval method also decreases admin workload in that:
1. Students will enroll themselves, filling out all the necessary + optional fields. The admin only has to look over the info and approve it.
Otherwise, students have to contact the admin to request enrollment; if the student neglects to provide required info, the admin then has to contact the student back for that info; then the admin has to create the account and email the student back to let them know it was created; and then the student will probably still have to fill in extra profile info or change the password.
2. Unlike the current email self-signup, admins don't really need to do anything about spammers. Whereas with email verification only, admins need to constantly check for spammers and disable their accounts & ban their IPs (and delete any spam posts), email verification + admin approval means admins can just ignore the spammers and not approve their accounts.
This is especially handy if there's a simple external list that admins can check the account signups against. E.g. if a signup's email address doesn't belong to a student or the signup's name isn't on the list of students, their accounts simply won't get approved and the inactive account will be deleted after a few weeks.
I understand that for large universities and the like, they'll usually have Moodle integrated with an external enrollment database, so they don't have this problem. But for small to medium-sized organizations, this is a vital account creation method that pretty much all other community platforms seem to support.