Retrospectives are a standard component of a typical Scrum workflow, and for good reason: they are a key element of an iterative, learning team. Feeding back input from developers and other Scrum team members is a great way of continuously improving their effectiveness, sprint over sprint.
Another important and valuable aspect of retrospectives is their role in granting team members real ownership over the process and their productivity as a Scrum team. A Scrum Master who is an effective facilitator can plant seeds in a retrospective that will bear fruit in the next iteration.
One way to do this is to be very clear about which “Needs Improvement” items flagged by the team will be tackled during the sprint, then diligently following through with implementation (ensuring sufficient story points are allocated to this activity, if development cycles are needed). Seeing their suggestions acted upon will encourage the team to bring more to subsequent retrospectives, creating a virtuous circle… and a more effective Scrum team.