As part of our checkout process, if you don't exist as a user in the system, you're prompted to create a username and password as one of the steps of the process.
Let's say this happens at the beginning of the process: you enter some credentials for your new account, click "Next", and continue with the checkout flow.
Now, let's say, for some reason, the checkout fails. (Abandoned cart, declined credit card, etc.) Should that user still have an account? Or is it confusing for someone to have an account despite their not completing the checkout process - the very process that prompted an account in the first place?
Should "user creation + order creation" be atomic? Is that more confusing or less confusing for the user's experience?
edit: in my particular case, I believe user accounts are necessary. We sell prescription eyeglasses - so as people upload prescriptions, it is necessary to store them "somewhere". Plus, in this case, customers will want to be able to check on the status of their order or shipment.