Sometimes customers place orders as guests not being logged in. And it might be a challenge to assign such orders to existing customers' accounts, so that all the information is located in one place.
Customer can place order using a different e-mail address and ask the store owner to move the order into the main account. Magento doesn't allow that natively.
Using the Reassign Order extension you solve the limitation. You can assign orders automatically to existing customers by email on checkout. Or you can reassign one or multiple orders to customer manually from backend.
Ability to assign orders automatically on checkout or manually from backend;
Ability to assign multiple orders at once;
Ability to override customer's name on order;
Full details in the order history.