Many MP players click behind a target unit or group when attacking, paticularly with the main infantry line. The thing is though, if you don't assign specific targets before they impact, you won't get a charge bonus. For defensive troops, like spearmen and byzantine infantry set to Hold/Hold, this can be desirable as their strength is in their defense, not their charge and attack. But for cav and infantry units with strong charge and attack factors, it's best to click behind your targets to get them to charge in formation, but then assign specific targets to each charging unit as they approach so they get a charge bonus.