In my view, Top 3 advantages and disadvantages of merging two approaches are as below :
Advantages
1. A combined approach ensures that both efficiency and effectiveness metrics are tracked and delivered as a package by the process excellence manager.
2. For senior management that is not too comfortable with statistics, lean brings in simple to comprehend tools and applications that are material to explain and easy to implement.
3. All projects, big or small, long term or short term can be brought under the purview of implementation by merging both the approaches.
Disadvantages
1. Process Excellence team may try to oversimplify or overcomplicate the project by not balancing both approaches.
2. It could lead to creation of two groups within the team - ones that advocate Lean, others Six Sigma risking the project progress on critical path.
3. Team members of Process Excellence team may need to get certified on both approaches which may not be seen as a welcome cost by the management.
Regards,
Tina