And metadata is far, far more than just what you've been searching for on the internet. Were you fatigued before an incident? If you say you weren't, why do your mobile records indicate a series of texts sent and received through the night, and can you justify keeping your job? Searching something on BeyondBlue, for whatever reason? Are you sure you aren't depressed? Say yes and you are seen as depressed, say no and you are seen as both depressed and lying to your medical examiner or CASA, both of which can have serious and ongoing implications for your employment.
Metadata also binds together a lot of otherwise separate information, which makes it so powerful. The tracking cookie on your home PC might know your browser history, the work PC might know you are a regular on the AFAP jobs website and pprune, the phone company knows who you call and when, and from where, the spyware you inadvertently installed may know your preference for busty blondes, but storing all this information collected across different devices and locations and collating it into one dataset, linked to you, for CASA, is far more powerful and dangerous than any individual organisation that previously had a piece of the overall picture.
Having an affair, or conducting anything else that you may not wish to be public knowledge but isnt otherwise illegal, there are plenty of pointers available through the metadata of when phone calls are made, or not answered (say late night calls that aren't answered when the wife's cell phone is logged in at the same location), when mobile phones log onto cell towers and when they move around from one cell to the next.
As far as claiming this helps stop crime and terrorism, TOR, VPN and numerous other forms of encrypted communication are already in use that effectively stop this form of tracking being useful, this is only a way to keep track of those people who arent seriously trying to cover their tracks; laws that everyone accepted in the name of national security are being twisted to watch everyone. People suspected of serious crimes will be surveilled, bugged by police or intelligence services following proper procedures such as obtaining warrants and otherwise monitored, this just watches everyone else that hasn't committed a crime (yet) until someone decides to leaf through reams of data and find something. Did your phone log onto a cell tower before you landed? But your company procedure is phones in flight mode, are you this neglectful of all your procedures or just the ones you disagree with?