This tutorial is adapted from issue https://www.drupal.org/node/1980974.
By default Commerce creates a Drupal user when an anonymous user completes checkout. If you have added fields to your site's user schema, it can be useful to populate them with the information the customer provides during checkout. For example, maybe you have added first and last name fields to users. If this information is entered during checkout, then you can avoid asking the user to enter it again when they log in.