The Governor General:
1. Represents the queen.
2. like a "Gate keeper" of passing legislations.
3. If he/she doesn't like what she sees cause it is not according to "Mother England's" wishes, then they will not pass it.
4. Has the power to dismiss/sack a Prime Minister they see who is unfit in their opinion, e.g. Gough Whitlam
Analyse... Personally I say,
1. The Governor General lately has had little impact on Australia
2. Rarely has the Governor Genera's imense power been exersiced
3. Protecting the constitution is more effectively done by the High Court through the separation of powers.
4. The governor general is just a way, not the way of protecting Australia's Constitution.
5. They would also make sure that it doesn't go against English constitution.
Hope that helps, google it. "Role of Governor General"