why does playing at home give +3 pt adv?

[ssmann]

hi all, this is my 2nd year betting the nfl. whats the reasoning behind giving the home team 3 pts?

[Limey]

In pretty much all sports, everywhere in the world, there is a statistically proven advantage to playing at home.

You could speculate about the reasons, but a recent book (sadly I am too drunk to remember the title) made a very strong case that the main reason is officiating. Referees are (unconsciously) influenced by the home crowd.