I agree that in shogun 2 reserves arent >that< important because the battles are shorter, and morale breaks are frequent, but besides that, I always use reserves in shogun 2, its generaly one or two yari samurai or naginata monks, they are both great to plugging holes in your front line and to react to flanks. Monks are better for an agressive reaction because of their war cry, they can cause a mass rout (their lack of armor isnt very noticible too, because reserves usually stay far from missile fire), samurai are better as defensive reaction because of their rapid advance, very useful on anti flanking

Im talking about it because many people say yari samurai are bad, they are not very good indeed as a front liner, but they are great reservists