From the introduction:
Power United is the second release from Devil’s Workshop focusing on team roles and relations. It examines a number of prominent comic book superhero rosters and defines members according to a system of roles in order to offer M&M players a better understanding of the makeup of teams from various comic book genres. Team training exercises, sessions in which characters may hone their skills together and improve teamwork, are also included, in addition to 19 new cooperative techniques, called maneuvers. Finally, Power United introduces strategy feats, battle tactics that can benefit everyone on a particular team. While Power United references roles and maneuvers from Power Assaulting, the first "team examination" book, the latter is not necessarily required. Power United simply offers additional options and observations.