Consider that you have a webform for the submission of customer issues or cases.
The Status field in the Cases module in the CRM is mandatory. However, webform users would not be aware of the value to be set on the field because it is CRM-specific information. So, you can provide an override value to the field and hide it.
Fields with an override value are automatically hidden. Such fields can be used to fill out information that is helpful to your team internally, and not relevant to the customers.