Getting better outcomes from the team. Simply put, a team that is willing to listen to other perspectives and to not take disagreements personally is going to reach better outcomes. On the first, research shows that the diversity within a team only translates to more creative outcomes if team members are prepared to feed that diverse input through their own positions. On the second, we now understand better that rare trick of how to transform conflict from a disabling to an enabling event: groups whose members feel free to speak out without being vilified can keep conflicts focused on task rather than relationship, allowing problems to be robustly interrogated and leading to better outcomes.
Pay attention when there is a change-up to team composition. If Carl is in charge of the team, he should know that the emotional responses new starters have to their supervisor has a significant effect on their transition into the team. Making an effort to give support and make them feel in good hands is critical. More generally, when individuals find themselves working with a highly talented individual it's easy to feel intimidated and under pressure to perform comparably - especially once you've started to become familiar to each other but before you've developed an Us over I mentality. Being aware of that emotional component makes it easier to get past it, by recognising what lies behind tensions and acting as a spur to get the team on the same page sooner rather than later.
Finally Carl might want to be vocal about whether the managerial set-up works for his team. Specifically, evidence suggests that job outcomes and experiences can suffer when managers regularly work remotely. If it appears that this is a problem for his team, perhaps he would like to have a word, with this study as backup.
A gift for Carl? How about a book of (workplace appropriate) jokes? A compelling model has been drawn suggesting that even minor incidents of humour in the workplace lead to virtuous spirals that can lift mood and create a better working environment. Here, I'll start you off: what's orange and sounds like a parrot?