If your visa express, one becomes an unlawful non-citizen. If you are an unlawful non-citizen, then the immigration department have no option but to remove you from Australia. The immigration department have no discretion in this matter. If you are unlawful, you must be removed.
To avoid the need to remove you, the Department introduced a visa which is called a bridging visa. This is a temporary visa which allows you to stay in Australia while your make your arrangements to depart Australia.
This all might sound quite straightforward to you, but it isn’t. There are different types of bridging visas, and further, no one in Australia actually understands how they work. The immigration official at your local regional immigration office has no idea as to when a bridging visas should or should not be granted. There is every chance that an officer at a regional office will give you incorrect information about your entitlement to a bridging visa.
Some bridging visas allow your to work while others do not. The department of immigration will usually deny you permission to work in an attempt to try to stop you from either appealing to the Migration Review Tribunal or for that matter, the Federal Circuit Court. Your have every right to work and further, the department of immigration cannot deny you permission to work.