Multiteam systems (i.e., teams of teams) are frequently used to deal with complex and demanding challenges that require several teams' joint efforts. Yet, achieving effective horizontal coordination across component teams in these systems remains difficult. Using insights from organizational behavior research, we argue that horizontal coordination between component teams can benefit if a multiteam system is composed of generalist members acquainted with the multiple functions present in the overall system (i.e., high intrapersonal functional diversity; IFD). At the same time, however, such IFD may have detrimental side-effects, because generalists' broad focus may distract them from high-impact, specialized activities (i.e., aspirational behavior). Building on insights from organization theory, we propose that coordination across a multiteam system's hierarchical layers (i.e., vertical coordinated action between a team tasked with system-wide integration and task-specialized component teams) is critical for reaping IFD's benefits while avoiding its costs. These notions were supported in a sample of 236 fourteen-person multiteam systems engaged in a realistic decision-making simulation. Our findings illustrate how combining insights from organizational behavior and organization theory can advance academic knowledge on multiteam systems and offer practical solutions for managing such systems.