Why do I? Well, if I'm in row 1 or 6, I have to except on the new planes (as mentioned above). The other time I will do it is if I wasn't upgraded and I am not in rows 6, 16, or 17. Why? Because I'm tall. And those seats are crammed together so tight that I need to be able to run my feet under the seat in front of me just to fit - something I can't do if my laptop bag is down there.