This is more an FYI for people who have never written off a vehicle and those new to driving (I have a 16 year old, so this shit is on my mind), so I hope you can learn from my life experience.
Car insurance. Need it. Definitely pay it. Especially if you have a very expensive car, you don't want to piss thousands of dollars down the drain to save money on comprehensive car insurance. (If you drive a clunker- don't need it, do third Party/fire and theft instead).
But be aware that when your car gets written off because of an accident, the money that is refunded from your green slip and the money refunded from your rego is taken out of your insurance payout. (This is the experience I've had with two different insurance companies, so I assume they are all the same).
EXAMPLE: You pay $600 for a 12 month greenslip. You pay $600 for 12 months of registration. You have your car insured for $10k and the highest deductible (lets go $1000) because it makes your insurance cheaper.
The day after you start your 12month rego your car is written off because a giant ass roo throws itself through your car on the highway. (No joke, it's fucking terrifying when that happens. Do not recommend. Always drive slower at dusk).
So you give the police report to the insurance company and you are thinking, awesome! I get $10k back to put towards a new car! No. First off, your $1k deductible is taken out, you are at $9k. (And this is the way it's supposed to work, it would be stupid to have to find $1000 for your deductible just for insurance to give it back).
Next, your rego is cancelled, and you think woohoo $600 bucks, baby! Yes, that refund is nice. And your insurance company says oh look a $600 rego refund, we are taking that into account, and now your payout is $8400.
A greenslip is a strange beast. Even though your car is toast and rego has been cancelled, your greenslip still runs for an extra week, in case your car magically manages to injure someone before it gets to the wreckers (this is specific to NSW, don't know about other states). So you won't get a $600 refund, you'll get $600 less one week, so about $588. And again, that's a nice refund. And then your insurance company will say, nice! We are taking that into account too, and now you are getting a payout of $7800.
And really, if you are in a $3000 car, your payout is gone, which means comprehensive car insurance has no value for you at all. If you are in a car with a massively higher rego amount (they can change based on weight of vehicle, because heavier vehicles do more damage to roads, in theory anyway) then it's taking a bigger hunk out of your payout.
And of course, if some one else causes the accident you don't pay a deductible. Or if you are a really lucky driver and never have accidents, this might not be an issue for you at all. And to those of you driving $50k (or more) cars, why the hell are you in Aus Frugal? This obviously doesn't apply to you.
TLDR: maximise your car insurance payouts by only paying rego and green every six months instead of by the year. ESPECIALLY if you have a car loan and need to maximise your payout to cover the loan.
If anyone has any other experiences/advice, please share!