Just a thought.
As it's in Oz, these maybe so that the top of the dash isn't bleached by the sun, a problem that could well occur and would look unsightly on a coloured dash. Maybe they are only meant to be used when the car is parked up, just like windsceen shields, as I can't see the point otherwise.
If that were true then why does it have ventilation holes for the windscreen clear? These people must leave these on their poor cars all the time