Very important, as a home team, you have the last say in the ninth in a tie game.
Plus the home team defense knows every nook and cranny of their playing field, how balls carum off of walls, how bunts react down the third base line, etc. etc.
I don't think it has a big impact in a 1 game situation. I look for more situations where a team has been on the road for a while and they are facing a team that has played at home for the last 10 days.