Unpublicized is the main value of the future AUKUS SSNs. That is as long range strike platforms for nuclear missiles to deter China.
Australia
is considered equivalent to a NATO partner by the US and UK.
Within NATO the US shares an estimated 20 nuclear weapons each to Belgium, Germany, Italy, the Netherlands and Turkey. These are deterrents against Russia. Europe's geography permits these weapons to be deployed on relatively short range platforms, fighter-bomber aircraft, dropping free-fall B61 nuclear bombs.
http://en.wikipedia.org/wiki/Nuclear_sharing
Australia's
requirements are for much longer range nuclear platforms - to put mainland China at
risk. Hence the plan for AUKUS by the late 2040s is to supply Australia with
the best nuclear weapon platforms, which are nuclear propelled submarines.
Only multi-mission SSNs (unlike huge specialised SSBNs) are affordable for a middle power like Australia. SSNs have the speed and range to
quickly be in striking distance of China's major cities (mainly talking Shanghai and Beijing). This is if China attempted to
attack or blockade Australia.
Within patrol areas considerably east of Taiwan, Australia's SSNs will mount 6 to 8 future submarine launched hypersonic missiles (SLHMs - first coined here) with a range of around 4,000km. These would be a generation or two after LRHWs. Missiles China would have a
great deal of trouble stopping quickly enough.