We use the Country information to calculate postal prices (where appropriate) and also to give you a rough idea of what the price will be in your local currency.
Note that if you are paying by Credit/Debit card, the charge will be made in GB Pounds, and your Card Company will convert this into the currency you are normally billed in (just as they would if you bought items in a store in any foreign country).
(There's more about this in our Help pages.)