Many teams have someone who backs up or assists another team member when they need help to accomplish their tasks. Today’s best managers know that backing up another member of your team could be helpful or hurtful to the team’s effectiveness. When team members have uneven workloads, then the costs of backing up a team member when needed are not high. However, when team members have even workloads, then the costs of backing up a team member are high. So, be careful when assigning a backup for tasks where the workload is roughly equal for team members, as this may actually hurt, instead of help, team performance.
Source: Barnes, C. M., Hollenbeck, J. R., Wagner, D. R., DeRue, D. S., Nahrgang, J. D., & Schwind, K. M. 2008. Harmful help: The costs of backing-up behavior in teams. Journal of Applied Psychology, 92, 1299-1319.