I find it varies from day to day. The better our communication and post battle wrap up the better we'll go in our entire session. Conversely, days when we're quiet, don't call out classes (we all have arenamaster, but on a good day we call it anyway), don't change tactics or one of us is tired (like me today, ergh) we go terribly.
I find it extremely important for meshing the team and focusing tactics. Getting fired up doesn't hurt those reaction times either.

I believe they mentioned this at Blizzcon.