The ESTA has several advantages for travelers from Australia.
The principal benefit is that registering with the system means that Australian passport holders can visit the USA without having to go to a US embassy to apply for a visa, which is a much longer process with more requirements than the ESTA application.
Overall, applying for the ESTA from Australia is a much quicker and easier process than traditional US visa applications thanks to a streamlined automated system.
The ESTA was implemented to increase security by running checks on travelers from countries in the Visa Waiver Program. Before its introduction, US Customs and Border Protection (CBP) could screen arrivals with a visa, but the ability to perform background checks on visa-exempt travelers was limited.
Thanks to the ESTA, visitors from Visa Waiver countries, like Australia, can continue to enjoy visa exemption for the USA, but the added screening helps CBP to prevent security risks and makes traveling to the United States safer.