Well sometimes I want to compare nuts to other things. I want to be able to picture how MUCH of something contains how much energy (like when figuring out what best to snack on without jeopardizing my figure :p). I also want to be able to compare the energy per price of different products, like when figuring out the most calorie dense option for taking a hike etc. These are just examples. All I'm saying is that a fixed quantity on every product makes some mental math much easier. Similarly how all price tags (where I'm from) have the nominal price of the product AND the price normalized to 1kg of weight.