Gaza, adding to what Gecko correctly stated:
Consider a handbag or bigger lying lose at your feet during take-off. The pilots decide at V-1 that braking is in order.
At that point, the forces applying themselves to your innocent piece of handluggage might turn it into a dangerous projectile being catapulted at very high speed through the cabin, easily capable of killing or seriously injuring a human being.
Hope this sheds some light on our seemingly neurotic behaviour............
