What is the impact of mergers & acquisitions on organizational structure?

I Mergers and Acquisitions the change starts at the top since both the organizations do have CEO's. Once they agree on who will be the CEO to lead the merged entity, they yse the advantages arising out of the expertise available in each positions of the merged entity. When this is finalised, the impact is as predicted when the chose the entities and their rightful position or power and influence in the organization. For different organizations it differes.