Allow different shipping and billing addresses
By default, Shopify sets the same shipping and billing address to the same address on the checkout page. The checkbox that allows customers to have different shipping and billing addresses is still on the checkout page, so customers have the option to enable separate shipping and billing addresses. If you would prefer that your customers have the option of entering separate shipping and billing addresses always, you can disable this feature from the admin instead of having your customers do this at checkout.
To disable this feature:
From your Shopify admin, click Settings, then click Checkout.
Scroll down to the Order Processing section.
Under While the customer is checking out click on the checkbox to disable this feature.