An organisation should be able to express the users it has, and the needs of those users that it strives to meet.
To begin to understand the total activity of an organisation, the only thing necessary is to enumerate all of the needs - both internal and external - that it strives to meet.
This idea extends to the services that are provided. Each service accommodates a set of user needs. By understanding the needs of the user, each service can identify the most appropriate way of measuring the success or fitness of a service.
The Government Digital Service's Service Manual entry on user needs is a good place to start learning about user needs, and how they use them.