There are only two methods of stock valuation allowed for interchangeable goods in Australia.
One is FIFO, the other is weighted average cost.
So I guess one reason that it's used is because there really isn't a whole lot of choice.
Since you guys haven't studied weighted average cost method, it is difficult to suggest reasons why FIFO would be preferred.
...I dunno... have you guys studied LIFO maybe?? (you can't use it in Australia... only in the US)
Specific identification method (the 'each individual item has its own unique barcode' method of tracking inventory) is only used for inventory that is not interchangeable - that is, stock that is, by nature, individually priced, eg. diamonds, antiques, second-hand cars.
In real-life, FIFO is used because it restricts a business' ability to manipulate its profit figures or overstate expenses (increase in expenses = decrease in profit = less income tax payable to ATO). For instance, in times of rising prices (inflation), if you sell your oldest stock first, but you pretend that it's the new stock that's gone first... your inventory is going to be understated, your expenses overstated, and your profit understated. So the use of FIFO is supported by faithful representation reliability when considering this perspective.
Additionally, during times of inflation (which is almost always), not only are you going to be paying more for your inventory, but you are likely to be *charging* more for it as well. So, it is more consistent if you are to sell the cheaper stock when you charge cheaper prices, and sell the more expensive stock (and face an increase in COGS) as you begin to charge higher prices. It keeps expenses and revenues more aligned, which is better for both relevance and consistency when you look at it from this angle.
It's also easier to apply than weighted average cost (less calculations), and (though accountants don't care about this) usually emulates real-life because most businesses sell older stock first before they put their new stock on the shelves. This is called 'stock rotation' - think about supermarkets... they want to sell the food with the closer use-by first in order to reduce wastage ('stock loss').
Anywayz... it's kind of hard to guess what vcaa is wanting from you guys... perhaps if you dropped words like 'cheaper', 'more simple', and/or 'reflects real life' you'll pick up the marks. I dunno... vcaa is full of morons... I have no idea what angle they're going for on this.
Edit: Sorry... I have trouble remembering all the VCE terminology... I think I used VCE words for everything else.