In the middle of a flight today from LAX-ORD, the seat belt sign was turned on and the pilot or co-pilot came out of the cockpit to use the bathroom. As soon as the pilot went back into the cockpit, the seat belt sign was turned off. It was perfectly smooth throughout this portion of the flight, so it was obvious that the seat belt sign was turned on just for the pilot to use the facilities.

Is this a common occurance? I never noticed this happening before. Since it was an A320 which does not have a gate, I wonder if this was done for extra security. It seems a bit extreme as it inconveniences many passengers who are nowhere near the cockpit.