When you play an event file, your webcam will be automatically switched on when the Start screen is shown.
This means that the webcam will remain switched on all the time, even when no one is using the system.
So what if you don't want the webcam left on when your system is not being used by anyone?
You will now find that the webcam is switched off each time the Start screen is shown.
Then when a user interacts with the system, the webcam will be switched on whenever any screen is shown that contains the webcam item.
So basically, the presence of the webcam item on each screen dictates whether the webcam is switched on or off during the event.