As far as I'm concerned wearing of seatbelts on board should be mandatory whilst seated
It is on some airlines, e.g. Lufthansa
moving around the cabin - something I always do on long haul flights - should be on the basis of a strictly enforced return to seat and belt up policy, as per the book
Some airlines encourage pax to walk around the cabin, from time to time, on longer flights, perhaps to reduce the risk of DVT?