I can imagine how mirroring each others’ feelings can be an effective, efficient way to get a group on the same page… when there’s a stressor, one person’s fear can transmit to others, and everyone becomes more alert; when it’s a relaxed time, one person’s happiness can feed others’, and bolster a group’s sense of wellbeing; when one person is angry about something, the others may more quickly join against that “something” if they become angry, too. I don’t imagine that it’s about managing emotions, or even entirely about empathy—I imagine it’s about coordinating the group, keeping the group in synchrony.
I see this mirroring backfire in other situations—for instance, when someone is angry at another person within the “group.” Instead of the mirroring-of-anger possibly uniting the two people against a larger common enemy, it becomes this feedback loop of escalating fury…
I can imagine that the mirroring-emotions would help with empathy—would give someone a literal taste of what another is feeling—but I don’t know enough about either to know how much or little they overlap.