Real teams are said to have properties which allow them to outperform combined performance of individuals comprising the team itself. If individuals interact within the team on deeper, meaningful level, they tend to surpass both quality and performance of workgroups — groups of individuals working towards the same goal but with little or no collaboration, focused on individual performance and goals.
There are many different theories trying to shed light on such phenomenon called emergence. With agile teams, we call it self-organization. Either way, it seems that it is really a trait of all complex systems in our universe and that we do not fully understand it. Yet, it exists and I say — take advantage of it! The team is always greater than the sum of its parts.
This excellent video from Kurzgesagt — In a Nutshell explains the phenomenon tremendously well: