The basic use cases can be narrowed down to Customer care and Notifications.
Customer care is usually initiated by the users when they reach out to the respective businesses. The customer care agents can reply with freeform messages or automated responses as desired. This conversation will be open for a span of 24 hours from the time of the first message sent by the customers.
On the other hand, Notification messages are usually unidirectional and is solely designed for the business to send relative alerts and informative messages to their users. Although, in this case, the messages must be pre-approved templates that are registered with the WhatsApp team.
WhatsApp restricts any type of marketing or promotional messages that a business aims to convey to their end users and such templates would be rejected.