Customers to your store are not required to be logged in (authenticated) or anonymous. To setup your site to always be anonymous, you would only have to delete the two rules mentioned here:
What is the difference between an authenticated and anonymous checkout?
There is not much. Both authenticated and anonymous users will still have to fill out any information required by customer profiles. Customer profiles are not user profiles (multiple data fields per user), they are uniquely assigned to each order (multiple data fields per order). This allows the same customer to have multiple addresses for each order and other types of situations. But this does cause a bit of confusion as the user expects their address to appear if they are logged in.
If you are curious as to what happens with anonymous users, you can checkout the following screens and read through each rule.
Customer information collected for orders on separate entities called customer profiles that are associated with the order through customer profile reference fields. By default the Billing information customer profile type just includes an address field, but it can be edited through the field interface to include any additional fields you require. These fields will automatically be visible on the related checkout pane for the customer profile.
Some modules define additional customer profile types, such as the Shipping information customer profile type defined in the Commerce Shipping module.
During a default checkout process, customers cannot reuse previously created customer profiles. A new customer profile will be saved each time, though modules like Commerce Addressbook bring simple and elegant solutions to help save your customers time.
Found errors? Think you can improve this documentation? edit this page