By being one of the first to stand up you are able to get your luggage faster (if any), skip a few rows down the aisle, get out the plane faster, and ultimately

By being one of the first to stand up you are able to get your luggage faster (if any), skip a few rows down the aisle, get out the plane faster, and ultimately get to the immigration line before everyone else. When flying to the US from the UK I would notice that this could sometimes save 1 hour+. The end goal is to get out of the airport as fast as possible, not just the plane. So the advantage is pretty significant.