If you're using the vehicle regularly for long or remote travel it's a good accessory to have.
I have a 130 litre main and 70 aux. Its there for avoiding mandatory fuel stops with dubious prices and fuel quality under normal circumstances and ensuring I can make legs where fuel availability is uncertain or non existent.
Like Narrangga, I also always had to carry an extra Jerry to make Katherine from Nhulunbuy and a number of other legs.
I was over carting extra jerries years ago and wouldnt hesitate to go a larger tank if affordable.
Jerries take up space inside, are easy to pinch outside and "throwing them on the roof" requires a rack, full or empty.
Fine if you have one. If they are full it puts weight up high and you have to climb up on a dusty/muddy car to get them. Its no fun when the car is slippery in the rain and cold. If your vehicle isnt muddy or dusty then you probably dont need either.;)
Most long range tanks are much tougher than the original and if your going to damage a long range tank to the point of being unusable you will have destroyed the factory unit also.
My two cents. There are "fors and against"
If you have lots of spare room and remote travel infrequently - go Jerries
If traveling remote regularly, regardless of space, I'd have the bigger tank.
I still pull over regularly for a break, I just dont bother with the fuel.

