Why Magento re-saves existing customer addresses during checkout?

Question

During the checkout process even if customer selects existing address form the drop-down the customer_address entity is being re-saved. Any idea what for?

Update:

It starts at Mage_Checkout_Model_Type_Onepage::saveOrder where the following code is executed:

$service = Mage::getModel('sales/service_quote', $this->getQuote());
$service->submitAll();

This submitAll calls Mage_Sales_Model_Service_Quote::submitOrder which executes the following:

$transaction->save();

This method loops through all objects of the quote(?) and saves them.

Update:

The most disgusting thing is that they are doing it for all addresses customer has. So if your visitor get 10 addresses saved in the address book all of them will be re-saved during checkout. Don't wonder why it is the most resource consuming part of Magento.