The overall retrospective is the only new and additional event in LeSS compared to Scrum. Product Owner, Scrum Master(s), team representatives and management participate in the overall retrospective. The focus in this event is to improve the overall system. 

If the focus of this meeting is to look mainly at inter-team “issues”, management might become bored (as the issues are “too detailed”), and might not participate in future, thus leading to a situation in which system improvements are even harder to discuss and initiate.
Possible topics of an overall retrospective are e.g., enhancing Definition of Done (DoD), aligning of job profiles to Scrum, align/eliminate incentivized personal targets, align/eliminate evaluation of team members/individuals, align/eliminate all Theory X elements, eliminate all identified waste. Those are often huge and non-trivial topics!

Why is the DoD discussed in the overall retro? Imagine Customer Documentation (CuDo) is not yet part of the DoD, thus the CuDo team members are likely to be organized as an own department with a manager (team lead) coordinating the work. Assuming that DoD should be enhanced so that the CuDO is included, it means that the CuDo people will be integrated with the already existing (development) teams. Will the manager be happy to let go of his “kingdom”? Likely not, and thus the upper level manager might need to be involved in such a decision, so that the CuDo manager will let go. In the end, the CuDo manager will very likely find a new home, and might even go back to the actual writing of the customer documentation.

This is a retrospective like any other retro, and the standard format can be applied. It is worth noticing that as those issues might be big, the organization will need a long time to remove them. It is advisable to not start too many parallel actions.