In some cases, it happens where the same customer has more that one account, or has a registered account, but completed an order as a guest.
Currently, we don't have a way to move an order from one customer record to another in admin, it's only possible with some creative database update scripts.
We sometimes have a case where a customer created a registered account, then a week later creates an order and checks out as a guest. When we try to register the guest account, that customer's email is already taken. It would be great if we could just move the order (or even shopping cart) from the guest account to the registered account, then delete the unused guest account.
Sometimes there are multiple customers accounts setup by employees of a company, where the actual customer is actually the company they work for. When multiple employees of the same company setup multiple accounts, then leave the company, the store owner does not have an easy way to consolidate the orders under one account for this customer.
This functionality would be really great to have.