don't even understand what value I will get out of it. No examples, no explanation? Ok e-commerce... and? what's different with http://www.drupalcommerce.org/

don't even understand what value I will get out of it. No examples, no explanation? Ok e-commerce... and? what's different with http://www.drupalcommerce.org/ http://www.drupalcommerce.org/ or http://www.shopify.com/ http://www.shopify.com/ or ... How does it differentiate?