I am not a Celtics fan but the game in Boston, in their arena 'Garden', makes me excited. It is like almost always excited to watch a playoff game in that arena, especially NBA Finals. I usually think in series like this, it is maybe the most important game of 7 games is the game three. The winner of game three always getting quite advantageous in my opinion. This game is also very important for the series. Celtics need a lot on the offensive side but with their home crowd probably as electrified as possible, they might get that extra push they need. They might be getting more from Marcus Smart, Derrick White, Grant Williams, Al Harford. But one thing is for sure, gonna be a great game.
It is obvious that Garden has a big impact on the players, but it is not really against Celtics or anything. By that logic Madison Square should be the same way, it is one of the best atmospheres to play as a basketball player, but Knicks has been bad for decades, and with such ownership will stay horrible for a long time as well.
So, I believe if Warriors lose, it will not be based on Garden alone, they are just not consistent all that much, Celtics are not neither. Like look at Heat series, they won one, lost one, and kept up like that, because they were inconsistent on their defense and offense together, could say the same thing so far this series as well.