It's a very useful function for anyone who needs to quickly talk to someone and doesn't want to fill their phonebook with unnecessary numbers.  This function allows the user to open the WhatsApp application and enter the phone number directly without having to add it to the phone's contact list.  In this way, it is possible to send messages to people who are not part of the contact list, such as, for example, a customer of a store who needs to be contacted quickly, a supplier or even an unknown number.

This feature is especially useful for anyone who deals with multiple phone numbers in their work or daily activities, as it allows you to keep a clean and organized list of contacts, without the need to add numbers that can only be used once.  In addition, the function also helps to maintain the privacy of users, since it is not necessary to share personal information with unknown people or who are not part of the circle of friends and family.
In summary, the possibility of sending messages to a friend on WhatsApp without having to save the contact is a very practical and useful function for those who need to communicate quickly with other people, without the need to add numbers to the cell phone's contact list.