The advantage to diversity in human groups is the synergy that results from the interaction. That is, the group provides a collective solution or product that is greater than the simple addition of each contribution would suggest. There are three factors that contribute to the synergy of the group.
Common Goals - Though sharing common goals may provide a group synergy, the complexities of the global environment typically make it insufficient as a sole contributor.
Common Identify - Individuals that share a common identity within a group have common knowledge and concerns about fellow group members. Though individuals within the group may have differing goals, tasks, and experiences, they unite through shared activities, stakes, and threats.
Common World View - In this scenario, individuals may agree on the available options, but differ in their preference for each option. Neighborhood community watch groups are an example. Those groups containing both diversity and a common identity are typically more effective.
Synergy is the "sweet spot" for diversity and group performance. If a group does not share a common goal, world view, or identity, diversity can lead to conflict and competition within the group. Competition creates a major loss of resources while synergy optimizes the diverse contributions of the group.