By having two different ways of being opened, you have lots of flexibility when it comes to ventilation. You can get airflow around the sides and the top when you open it via the bottom hinge with no drafts! This is a huge advantage. This is because you can also open it completely and ventilate a room very quickly in this way. On top of being able to ventilate your home while you’re away without much risk, no water will enter your home if it rains!