Working with people you like, trust and respect can be fun, but how does having friends in a workplace team affect outcomes? Social incentives only work some of the time – they are not a "must have" for more productive teamwork, new research suggests. Leadership, effective management and well-designed teams are key, while the presence of high performers on a team also has an impact. But "superstar" team members have both positive and negative effects on their colleagues. Why? Because bright, shiny people who perceive they're contributing more than others may try to redress the balance – or even opt out altogether.