I've always been of the opinion that the rule exists only partially because of the possible dangers of RF interference with avionics. It has been tested here and there, just not comprehensively, and it seems that modern aircraft systems are pretty well shielded against interference from common phones and laptops.

Why is it that we are required to fasten our seatbelts during takeoff and landing? Why are all pax and flight crew required to be seated, and not in the lav, galley, or isle? Why must the seat backs and tray tables be put in the full upright and locked positions? Why must all carryons and loose articles be stowed securely under the seat or in the overhead?

It's because takeoff and landing have the most instances of actual maneuvers. Turns, banks, climbs, and dives are all routine parts of takeoff, ascent, descent, and landing, even when the air is perfectly still and there is no turbulence of any kind. Securing loose articles, and people, during these maneuvers, gives pax the highest possibility of escaping injury in the event of an incident, and prevents loose articles from flying around the cabin when the aircraft banks, rolls, or pitches.

I obey these rules, not because I'm a mindless lemming who always does what I'm told, but because I'm intelligent enough to see the very real risks associated with having loose articles in the cabin during takeoff and landing.

I also keep my seatbelt fastened whenever I'm seated during cruising flight, because you never know when sudden, unexpected turbulence might make the aircraft do a Ringgold's Pirouette and turn the cabin into a giant cocktail shaker.