Assigning contact owners will update "Seller" info on automated statements and invoices.
When automated statements and invoices are sent out, they include a "Seller" info section. Assigning someone as the contact owner will make sure those statements and invoices being sent out have this employee's name as the seller as opposed to your account's default settings.
All employees will be able to see and access these assigned documents; it is not a hard rule of ownership.