Why did Malcolm tell every soldier to break off a branch and hold it in front of him?

Malcolm instructed the soldiers to break off a branch and hold it in front of them as a means of camouflage, allowing them to disguise their numbers as they approached Dunsinane. This tactic was intended to mislead Macbeth's forces into believing that they were facing a larger army than they actually were. The branches served as a visual cover, helping to enhance their strategic advantage in the impending battle.