Aggresive Stance: Henchman will attack at will.
Defensive Stance: Henchman will only attack if they get attacked
How this could help in some situations:
Need to pull with a bow, but cant cuz henchies will run in.
While holding an item (ex. ashes) you cant tell your henchies who to attack, so they will randomly attack any of the enemies.
Thats just 2 small examples.
I think its a great idea, seeing you will be in different positions at different times. Hopefully ANet reads this
