Actually, there is an advantage. When a left shot goes in on left catch goalie, a the player's stick side lines up with the goalie's stick side. In this situation, the stick side is easier to shoot on than the glove side and is the tougher save because the left shot player can create better angles.
In addition, players naturally expect to face left catch goalies. When they face a right catch goalie, it throws them off. All their instincts about how the goalie is positioned, where their stick and glove are, will be wrong.
Goalies line up to the puck, not the body. There shouldn't be better angles on one side than the other if you're positioned correctly.
That second part may have some effect though.