David Gooblar explains in this piece why he uses self-assessment at the end of the semester with his students.

There are many reasons to have students complete self-evaluations at semester’s end, but perhaps the best is that the exercise encourages metacognition. (…) metacognition is a significantly valuable tool at the end of a course, when there are so many opportunities for self-reflection. At that point, students have been working on the same subject for more than three months; before they move on to other courses, and other professors, give them time and space to reflect on what they’ve done, and how they’ve done it.

Gooblar offers several techniques to stir up this metacognition among students. Those techniques can be up-front about the end goals, but they can also be more subtle in approach.