The most helpful feedback I received was during bedside preceptorials, when our preceptors would ask us to perform the physical examination and they would give us constructive advice until we got it right. Reflecting on it now, even if this was in the early 2000s, our preceptors were practicing outcome-based teaching already.
The least helpful feedback was being given the answer key to MCQ exams, with no discussions about the items, and sometimes without even a copy of the questions. This was just pointless and I felt they were just giving "feedback" to comply with college rules.