A motion-sensor light near the entrance or in a dark corridor does two useful things at once. When you come home with your hands full, the light turning on automatically feels like a warm welcome and helps you find keys and locks easily.
At the same time, it can startle or discourage anyone loitering near the door. People who don’t want to be seen don’t enjoy sudden light shining on them. Even a simple sensor lamp sends a message that the area is watched and active.
You don’t have to remember to flip a switch every time, and you’re not wasting electricity by leaving lights on all night. It’s convenience plus a small security boost in one go.