Optimization principal 3: Minimize the number of enabled objects in a scene. Sometimes we may not want to completely remove an object, but we can identify times when a scripted component of an object can be safely disabled. If a
Monobehaviour script is disabled, then Unity no longer needs to send the object
OnGUI() messages for each frame.
For example, if a non-player character (NPC) should only demonstrate some behavior when the player can see that character, then we only need to be executing the behavior logic when the NPC is visible—the rest of the time we can safely disable the scripted component.
Unity provides the very useful events