I have never bought two seats but whenever I fly with Emirates from a domestic airport in the UK I almost always have a seat next to me free, sometimes even have all four seats in the middle free which means I cna lay down and sleep all the way to my destination (i did this on a flight from SIN-MEL just recently) i have noticed that whenever i fly in teh US the plane is always full with people waiting on standby nearly all the time, even once had to have some people give up their seats as it was overbooked but have never seen this happen in the UK or anywhere else as of yet