At any given period lessons learned illustrates what worked and did not on that particular project. While lessons learned should take place throughout the entire project life cycle. While this happens throughout the process, lessons learned can only be fulfilled at the last part of the project process.
Why are we having a lessons-learned documentation when it cannot be used for the betterment of the existing project? The reason is that most of the projects have similar mechanisms, components, and characteristics with that of the previous ones.
Lessons learned are at its greatest importance when they are (a) documented, (b) shared, (c) archived, (d) made flexible to allow modifications in the conclusions. Take time to analyze these lessons learned, and observe your project being lifted to the pedestal of success.