The Retrospective is a critical part of succeeding with software projects. I have seen many teams ignore this and as a result be less effective than they could have been. Other teams that do retrospectives just use it as an opportunity to say what went well, what didn’t go so well and what could be done better next time without actually doing anything to improve their process.
In the LeSS framework, you will undertake two retrospectives. The first will be at the team level where individual teams inspect and adapt their ways of working and processes, and the second will be at the product level where all teams (or suitable representatives from all teams) gather to inspect and adapt the whole system.