With Empowered Spell if you roll on your two D8s a 7 and a 6, you can reroll the 6 in the hopes of having another 7 chaining it to another target, and if you say roll an 8 instead you can reroll the 7 in the hopes it becomes a matching giving you another chance to chain it to another target.
And if that works and you still have damage rerolls left, you can reroll the D8s on the next target too, possibly getting a third, may be a fourth, target his hit by the spell. Makes the spell more interesting.