well from the cabin crew point of view landing and takeoff are when you want the pax to be a little aware of whats going on around them, and if they are playing with electronic gadgets ie, cameras .phones and the devils instrument the Blackberry then they could be slow to react to a situation developing. About a year ago had to rapidly disembark an aircraft and was amazed at how many people were turning gadgets on as they got off!!!!!! they were actually putting there own safety at risk just so they were contactable in the morgue!!!