I had just posted something similar in the game thread but for these two ATL games, Horford has been the X-Factor in my mind. His importance is amplified because we don't have as much depth at his position as other positions. You can take White out and put in Brogdon, for example. But Horford has been critical. We are +36 when he has played this series and -10 when he is out.
Brogdon has had a great +/- also (+25) but he is shooting 29% overall and 1 for 7 from 3. Smart and White have both been excellent, both box score and +/- or NRTG. But I think Horford has been more important than any of these 3.
Horford brings another element that I think is also very important. It is kind of a steadying or calming influence that he brings. There was a point in the game where ATL called a TO after we went on a little run with Horford making the last basket. As the team was heading off the court, all the young players were jumping around and doing high fives or chests or whatever. As they worked their way to Al, he was just walking off the court, total game face, offered simple high fives, and you could see the rest of the team adjust and adopt his more laid back demeanor. His body language sent a message to the team. Still work to do here. Stay focused.