Shopify uses headless commerce to overcome the limitation of traditional Shopify architecture. The main difference between Shopify and headless Shopify is the former doesn’t give enough customization opportunity, whereas the latter maximize customization and personalization opportunities. 

The second difference is it’s hard to produce an omnichannel experience in traditional Shopify, whereas headless Shopify builds a great experience across the channels. Shopify also uses headless commerce because it wants faster time-to-market stores by removing the dependency between the marketers and the developers.