For the math & physics classes, the deadlines are 3 weeks after being assigned, whereas when you take the class in person, there's a strict 1 week deadline.

Part of the advantage of taking an online class, as opposed to self study, is the motivating factor of deadlines. I have a lot of textbooks I've started reading, then said "I'll get back to this" and never have.

Another advantage of class over just textbook is discussions with classmates and TAs. Having a schedule helps with that too, since there are others working on the same material at the same time.