Fn_Calculate_Cart_Content : Calculate_Shipping

Does this even do anything?

As far as I can tell the only place where calculate_shipping is on the same line as 'A' anywhere is in the function's definition. So for example, I can't find anywhere in this function where 'A', 'E' or 'S' is actually checked.

To me it looks like wherever calculate_cart_content is called, it's called once and then called again, I'm not sure why this is. Any ideas?
It seems a little wasteful to calculate every enabled method for cases where you want to use one particular method (particularly something that doesn't request external APIs to get the cost).
Is it possible to calculate the value of an order for only a given shipping method?

Further clarification: my question comes from the way Tygh/Api/Entities/Orders.php's create() works