There are many types of units in an army. The bigger a unit, it is also possible to be multiple types of units within a larger unit. This gives an army more options to fight as every type of unit has his strengths and weaknesses. The difficulty for a unit commander that has multiple types of units in his unit is to realize these strengths and weaknesses and utilize them to there fullest. Also the strength of an individual unit can increase or decrease depending on how good different units communicate with each other.