Clark Quinn discusses linear versus self-navigation in the first of a series of "Broken ID" posts.
One of the benefits to self-paced content over class-room, is that the learner can review the content in a way that makes sense to them. By doing this, they can gain some ownership over the material.
Courses that lock a user into a "click next" linear flow, are forcing all learners into the same mold, regardless of their prior experience, acuity, or understanding.
Imagine if you had a text book that only allowed you to turn to the next page, or back to the prior... would that really be the most effective way to utilize that resource for learning?
Yet it's done all the time in self-paced elearning courses.
Clarks states:
"The point is, while a good default is a reasonable choice, having some alternative paths might be worth considering, and allowing learner navigation is almost essential. Allowing learners to test out is a good option as well. Don’t lock your learners into a linear experience, unless you’ve really designed it as an experience"