Motion detectors have been attached to the lights on the outside of our homes for decades. Sure, they are somewhat effective because burglars don't like bright areas, but they've been around so long that they do nothing more than shed light when tripped.
But with a smart home you can have a motion detector on the outside of the home trigger things on the inside of the home!
Imagine a would-be burglar snooping around the outside of your home at night when you're not home. Sure the motion lights come on, but he's not phased by that. Then he trips the motion detector that talks to the rest of the home. That can then set in place a series of events that can include lights turning on in the room nearest the activity.
Now the would-be burglar thinks not only that someone is home, but that he was heard and that's why the light on the inside was turned on.
Thieves would rather enter an unoccupied home, so give them every reason to think you're home, even if you haven't been for days.
You can also get a text message when that motion detector is triggered, and the alarm is set to Away mode, so you will know to check the cameras on the exterior to see what is going on right away. Then call the next door neighbor and ask them to peek over the fence, or start turning all kinds of lights on from your phone to make the burglar think the house is full of people.
All of this and you never had to leave the dinner table.