The success of Wikipedia has demonstrated the power of peer production in knowledge building. However, unlike many other examples of collective intelligence, tasks in Wikipedia can be deeply interdependent and may incur high coordination costs among editors. Increasing the number of editors increases the resources available to the system, but it also raises the costs of coordination. This suggests that the dependencies of tasks in Wikipedia may determine whether they benefit from increasing the number of editors involved. Specifically, we hypothesize that adding editors may benefit low-coordination tasks but have negative consequences for tasks requiring a high degree of coordination. Furthermore, concentrating the work to reduce coordination dependencies should enable more efficient work by many editors. Analyses of both article ratings and article review comments provide support for both hypotheses. These results suggest ways to better harness the efforts of many editors in social collaborative systems involving high coordination tasks.