I agree with 2 of the previous posters.
1--At my house, it's a free for all. Grab a plate, slap some food on it, find a seat and chow down. LOL
2--I would rather sit down and converse with people you don't see or talk to everyday. That way you get to catch up on things from other parts of the family.
While it looks nice to have the table all set and pretty and with the candles, flowers, place cards,etc.....I think some people do it for the look of it (looks like something they saw in a magazine or something) LOL But in reality, I don't think most people really enjoy being told where to sit. I think if Aunt Betty doesn't like cousin Billy Bob....they automatically won't sit near each other.
But everyone has their own way of doing things and that's why this world spins the way it does. IF everyone was exactly the same, it would stop on it's axis, I'm sure. LOL