If you select an assignee for a contact (in the contact details page) and the assignee has an address, it will automatically copy over to the contact's address. Please note, this will not overwrite any existing contact address information. It will only populate the assign address if the contact address is blank.
We have spoken with engineering to link the assignee address to the contact address, such that changing the assignee address will automatically update the contact address.
We will update this post when this has been completed.