In some operations, the owner of the company wants to retain full control of the account, but would also like the ability to designate an additional owner who can make account-level decisions when they are unavailable.
That provides better coverage and redundancy, particularly in situations where the primary owner is out of the office, unavailable at a critical moment, or leaves the company altogether.
Having a secondary owner or equivalent level of administrative authority could help reduce dependency on a single individual while still allowing the organization to maintain appropriate control over the account.