Leadership can be important for a team that will be intact for longer-term assignments, including major projects. This need for a leader can provide an opportunity for someone new to rise to the challenge when a team is composed of "social loafers," to borrow a phrase from a recent Faculty Focus article. For a more heterogeneous team that includes social loafers and proven leaders, it is not overly surprising when social loafers continue to sit back while other group members take the lead. Might this be an argument for forming homogeneous teams from time to time?
Of course, "homogeneous" can refer to a variety of characteristics. Forming groups based on similar opinions can yield different results compared to groups based on similar skill sets. One approach isn't necessarily better than the other; as stated in an earlier post, the best way to form groups largely depends on what the groups are being asked to accomplish. Barkley, Cross, and Major (2005) point out that grouping students by skill level may be particularly beneficial in language and math courses, for example; the similarities are likely to foster communication among group members since they share a common starting point.
There are potential drawbacks to homogeneous groups, and these downsides are neatly packaged into arguments in favor of forming groups that are heterogeneous. Groups that include students with a range of skills, for example, may be better prepared for a variety of tasks, and heterogeneous groups are likely to expose its members to a greater variety of backgrounds and/or experiences vs. homogeneous groups (Barkley, Cross, & Major, 2005, p. 45). Sometimes heterogeneity can lead to disagreements among group members if they are approaching an issue or problem in different ways (which is not necessarily bad depending on the intended outcome!), and/or it may generate some unintended consequences if students are isolated from others with similar backgrounds (gender, academic ability, etc.) that may provide helpful support. Note that if these potential downsides of heterogeneous groups seem to create too many hurdles, it may be worth (re)considering homogeneous groups based on the characteristic that is most important to clump together.
For instructors using groups for shorter-term, lower-stakes opportunities, switching back and forth between homogeneous and heterogeneous groups is always an option too! For long-term groups focused on higher-stakes assignments, keeping groups intact for as long as possible is the general recommendation since it fosters trust between members.
Barkley, E. F., Cross, K. P., & Major, C. H. (2005). Collaborative learning techniques: A handbook for college teaching. San Francisco, CA: Jossey-Bass.