Just because a location is unoccupied doesn't mean it's safe to leave it unsecured. Besides the risks of people sneaking in to steal, take photos, or plant bugs, you also have stalkers that range from "I just wanted to meet my hero" to "I'm already in your bed, so we're going to have sex or I'm accusing you of rape" to "Your skin would make a nice jacket." They probably do have on call staff, but realistically he has 3-5 guards assigned to him specifically at all times with 24/7 coverage of key locations.

And you're correct about chilling out and learning on the clock, it's kinda how I got my current gig. Most just watch Netflix though.