Depends on the C-title and the jurisdiction. There are legal documents that can only be signed by the CEO. Some actions of CEOs need to be published immediately in case of public companies. So it's the duty of the real CEO to prevent other people in the company to make outsiders think they could act in a certain way on behalf of the company.

CEO I understand, also other officers that are legally bound (possibly the CFO for reporting financial results for instance, or the Secretary).

But then there is the plethora of Chief Marketing Officer, Chief Information Officer, Chief Whatever Officer which are being created more or less ad hoc.