Such a team has a reasonably amount of voluntary turnover. Too little turnover and too high turnover create different problems. Either teams stuck in their ways, overly rigid in roles, and overly dependent on certain heroic members, the org is terrified to lose. Teams with too much turnover lose valuable experience before it can be passed on.
In my mind good teams are teaching and learning machines: members adopt new/different ideas, different roles, new members, by being given safe space to fail and be curious.