Who cares about the 2nd unit? They'll get like 13 seconds of ice time each PP.
I care, the whistle doesn't blow when the PP runs out. If you don't score on the first PP, having an effective second PP can keep the other team on it's toes and disjointed as you transition over into even strength.
Also, Sergachev had himself a nice rookie campaign in large part because of the second PP unit. There is opportunity on the second PP unit, but it might not always come during the actual power play.