Turning Is Active? off marks the state as inactive: it is shown with an INACTIVE - prefix in the admin States list, and it is removed from the state dropdowns customers see – both the shipping-address State dropdown on checkout and the "see what days we deliver to your area" delivery-area search only list active states. It is not removed from every internal list (for example, the order-confirmation page still loads all states), so an inactive state can still appear on pages that were not customer-address forms. To fully stop deliveries to a state, also remove or deactivate its zip codes and routes.