It would typically be used for extra storage as well as an open work surface for paperwork, filing, or other tasks taking up more room than would be practical at the main desk (often due to the presence of a computer).
An executive desk is often the central artifact for a meeting between several persons.
A computer monitor or a printer or even a simple keyboard on the surface can be impediments to the exchange.
When its planned use is to be less frequent, such as holding books or files which are not regularly referenced, or to act as an extra surface to help facilitate larger meetings, credenza desks are often placed on a wall in some other location of the office, such as adjacent to a conference table if one is present.
Credenza desks are often, but not always, part of a matching set that can include pieces such as a primary desk, a conference table, a cabinet for a whiteboard, a bookshelf, filing cabinets, chairs, or other items of furniture which are likely to be found in an office environment.