I've heard that before. The way I understand it:
If after dinner you eat nothing before going to bed, you will go to sleep with a more or less empty stomach. Your body restores during the night, which takes energy. So drifting on your last dinner and nothing extra probably creates a slight deficit, especially since the 'snacks' we tend to take are high in sugar or fat levels. This may in some cases help losing weight, especially if you take a walk before going to sleep and before breakfast the next morning.
It's probably a lot more complicated than this. I'm not sure if this is either a correct explanation, or the right thing to do.