The last phase of a project should enrich the knowledge base of all participants.
In every project, new ideas surface. New approaches may emerge which will enhance the next project.
These insights emerge in both successful projects and projects that have great difficulty. The common approach is to spend more time on an analysis of poor/troubled projects: "How do we avoid that mess again?" But, often, a clear analysis of well done projects can enrich the management of all future efforts.
Subjects for learning:
These ideas are often extremely valuable. But, only if time and effort is spent on reflection, documentation, and dissemination.
There are always new possibilities to discover and better ways to design...