well, here's the thing. The structure tells you when to use it - when you need to access the most recent item put into a group.
In business accounting, there are two main methods used for keeping track of inventory costs. First In, First Out (FIFO), or Last In, First Out (LIFO). Say I buy 100lbs of steel at $1 per pound. a week later, I buy another 100lbs of steel at $1.15 per pound. The next week, I USE 80 lbs of steel. I want to record the expense of my inventory used to make $100 worth of my product. I could use FIFO, and say that steel cost me $80. That gives me a bigger
profit today of $20 ($100 in product - $80 in material), but also leaves me with more money tied up in inventory ($20 of $1/lb steel, $115 in $1.15lb steel == $135) of materials not being used.
OR, I could use LIFO and say that steel used cost me $92 (80lbs at $1.15/lb). Now my profit today is less ($8), since my materials cost a bit more, but I have less money tied up in inventory (20lb * $1.15 + 100lb * $1/lb == $123) .
If i recall correctly, a business can use either method of LIFO or FIFO, but once they pick one, they have to stick with it.