I run an entirely online writing program for gifted kids. We use Moodle and email as two different formats of the same courses.
The virtue of Moodle is that assignments don't go astray, land in the spam bucket, or just vaporize.
Recordkeeping is immensely easier. The gradebook can be as simple or complicated as you wish. We use a simple system of [no grade] = not yet turned in, 0 = unacceptable or late, 1 = worked turned in & critique has been posted.
Messaging keeps a record of anything everyone says. Emails go out, but the record remains in the classroom. So, when Johnny makes a promise, it's there for everyone to see.
If you need to substitute or replace an instructor, all that has happened is there to be seen. In a purely email course, you would have to find and forward immense numbers of messages.
With advanced uploading, any changed or additional files are all in one place. With email only, you may start working on an assignment only to discover 40 emails down that there's another version, or that a missing piece has been sent separately.
We find Moodle's main classroom page a blessing. Students start at the top and "fall" down the page till the course ends. We rarely get "what's my assignment? where do I find it?"
If you need to make changes to an assignment, you don't have to rely on an email to all your students actually arriving in all your students' in boxes. You make the change in one place where it can't be lost or vaporized.
So, why does my program have both an email and a Moodle format for one course? Because the email format doesn't use forums for workshops. Web-based work takes more time because of the social aspect.