This is from the first tutorial battle:
As you can see Triarii unit keeps its formation and doesn't enter into enemy unit to kill them fast. This small skirmish lasts longer than it should be. In the first Rome Total War, units behave like this when they on guard stance. When they are not on guard stance they go to penetrate and surround enemy units to kill them faster. Now, we don't have this button. Due to critisism over months for blobbing units, CA made units protecting their formations more and more.
This is an another example from a custom battle, Triarii units went back to their formation after clash with enemy:
Most of them waiting while few of them fighting in the front line.
If we have "guard" button we can choose how our units behave:
- Keep formation with guard button
or
- Push, penetrate, surround enemy unit without guard button