Unit formations can be a very good addition to Samurai Wars. It will make the game even more strategic and realistic but not more laggy either.
Lets just say when you click the unit there are some icons in the screen which can activate formations. The most basic formations that have the potential to be added are:
Tight formation where soldiers inside the unit cramp up just aside each other and take more damage from ranged units but are affected less from melee units.
Loose formation where the soldiers inside the unit just get a little far away from each other and take less damage from ranged units but are affected more from melee units.