As a merchant, can you imagine all of the benefits with allowing your customers register with Facebook or Twitter?
Customer Information - This allows you to capture the email addresses before they ever get to checkout and other additional personal information that your customers don’t mind sharing, but definitely don’t want to have to fill out another form for it.
Commerce Guys provide many screencasts around the Drupal Commerce ecosystem to demonstrate how you can easily extend your store using contributed modules.
This tuesday, let's talk about Commerce Customizable Products which is another module that provides custom line item types like Commerce Custom Line Items.
Watch the screencast.
Find more videos at DrupalCommerce.org