Have a look in the Expanded rules book for “Enfilade Fire”.
If you get a unit adjacent to an enemy unit then during your assault phase you can say that that the enemy unit is preoccupied(and therefore facing) your adjacent unit. Then if any other units can trace a line of fire into the rear of that enemy unit they get a plus one on their rolls.
Of course if you surround an enemy with adjacent pieces you can dicate where the facing is so that each of your pieces gets the bonus.
Happy New Year folks. May you have plenty of gaming time!