Previously a Shop would have to create/purchase a shipping label before an Order could transition to Fulfilled because the Customer chose Shipping during checkout.
This new button,
Mark as Fulfilled without Creating Shipping Label will bypass the creation of a shipping label and mark an order as Fulfilled. If the Customer changes their mind and now wants the Order shipped, no problem. Simply change the Order's status to Unfulfilled and you will then be able to
Create Shipping Label again.