> Presumably because the price is a volatile, and storage gives you more flexibility around when you buy.

I will give credit to the person who got there before me. :)

Smoothing out price volatility is a big one.

But also it gives you options:

You can buy it "today" when its cheap and store it for when you need it (e.g. winter months).

You can also trade on that basis too. For example you can make a future-dated commitment to buy gas (knowing you have the storage available to take delivery). But if the situation changes and you later find you don't need it, you can sell that contract to someone else (or you can still take delivery and re-sell it). But you can't do any of that without having the ability to take delivery, because the person who sold you that future-dated contract will want both your money and to get the gas they sold you off their hands.