Every business is unique. Your business may be dependent upon an internal system and may have specific requirements. This could be to interface with your intranet, or for it to make a call to an online service or something else!
You may also need to define internal processes, and who has access to what screens in your application? For instance, the data entry team can enter data but cannot approve or delete data. In contrast, System Managers can enter or approve data but can't delete, leaving only Administrators with the rights to delete.
Defining your requirements helps to identify the behaviour, attributes and properties of the future system. Therefore, the main task of any functional requirement document is to ensure that all stakeholders understand what is needed and what is expected.