Salesforce allows order creation without adding any product into it(product can be added later). I am unable to get a real life example where we create an order without adding any product/service/contract into it. Maybe I am thinking in particular e-commerce scenario only that's why I am unable to think any use case for it.
A similar question has been asked earlier, though I am still confused with some use case.
One of the answer by Cheryl Feldman there states an example of transactional order for a change in billing or billing contact. Should that be counted in order?