Bathroom exhaust is not there for the sole purpose of stopping your mirror from fogging up!
Bathroom ventilation is required to remove moisture and odors from the room and eliminate moisture build-up which could otherwise result in mould and mildew problems.
The Building Code of Australia (BCA) enforces Australian Standard AS 1668.2-2012, which states a minimum extraction capacity of 25 litres per second for residential bathrooms. Although the minimum level is 25 litres per second, a majority of designs are produced requiring a level between 50 and 60 litres per second.