I believe the landing lights during daylight have a selection for the lights to flash. This makes the aircraft much easier to spot in a terminal environment by controllers and traffic. Landing lights are used during the day only to make the aircraft more visable, and serve no other purpose. The flashing makes the plane much more noticable in my experience.
Enroute at flight level I will flash my landing lights at oncoming traffic comming the other direction on the same airway at night. At different altitudes of course. This is a common practice.
It is also supposed to prolong the life of the bulbs. They are not actually turning off, just dimming significantly. This prevents the filament from shock cooling and as they are not constantly on full power the bulb lasts longer.
I've seen it done from inside the aircraft. It is very noticable when you are in cloud at night, because the whole cloud lights up. At first I thought it was lightning, but lighting flashes are more irregular.