"We do not learn from experience. We learn from reflection on experience."

 John Dewey. 

The reflection from learners and instructors should be on what is being learned and why. Although learning can be informal, it should also be an explicit part of a project. Reflections does help students solidify what they have learned and think about how to take it beyond the project.

Overall, such reflection helps both students and learners. Students can decide how they might approach their next project, and helps teachers improve the quality of their PBL practice.