Joint action research – the field of research investigating online-coordination during task performance between groups of participants – has uncovered a prominent role for the coordination pattern of synchronization during joint task performance. From the coordination of basic motor and perceptual processes to the foundation of efficient task performance and group cohesion, synchrony seems to play a crucial and beneficial role. However, some recent findings suggest that synchrony is not always beneficial for joint task performance and subjective wellbeing. The current proposal seeks to investigate the boundary conditions of synchronization’s beneficial role in joint action. Particularly, the hypothesis is put forward that behavioral synchronization during joint action is beneficial for comparatively "simple" tasks, but detrimental for complex task, that is, tasks with a high degree of uncertainty and a high degree of action options. Across several studies, this hypothesis is tested and the goal is to develop this hypothesis into a more encompassing theory of the role of synchronization during joint action.