that home field advantage has its perks. A lot of that is due to familiarity of the environment (stadium, routine, home, etc). Some of it is due to the fans. Vegas considers the totality of those effects to be worth 3 points on average. Hard to say how much of that the fans contribute, especially as it's going to vary game to game and no one knows which games will have that big spark to create that fan-team symbiosis.