"Empty Seat decision will be emailed (4-72 hrs) before departure"

I assume they just look at the empty seats on the plane and arrange seating so these requests are fullfilled.

I'd be intrigued to know how this impacts other passengers. Does their assigned seating get rearranged? Also how is this different from changing your seat assignments at check-in to the get empty rows / seats.

Would be a great option especially on Long Hauls.