To make my point more concrete in terms of your example, the benefit would be something like:

Let's say Iceland has some natural advantage in fishing, because of the great fish around there. But, because our world violates the law of one price, it's instead of profitable to smelt aluminum there instead of fishing[2], and the world is deprived of the utility gain from the fish captured and shipped[1].

But then, once the world obeys "one energy price", the smelting doesn't make sense and they go back to fishing (while the imported crypto miners sop up the extra energy).

[1] hopefully with sustainable management

[2] They still fish there, today and in the hypothetical, but probably much less than the optimum.