The big hosts have been doing this for years, and now you can too! OAuth Pro gives you the ability to release an API to your clients.
This also gives you a completely new way to access the WHMCS API. Rather then using an admin account sending out your username and password, which sometimes is not practical, you can perform your API requests using OAuth instead. Protecting your admin username and passwords.
Another advantage to using this method is that you have complete control over what keys can execute what functions. That's right you can now allow or deny specific API functions from running with the OAuth keys!