We use it to notify our upgraded users with emails or forum notifications when they receive a new message in their exclusive threads (we do personal consulting in these threads). Since XF default behavior doesn't keep notifying users about a new message in their thread if they haven't viewed the latest comment, many of our messages were missed and the service we provide was not that great. This add-on solved this issue for us, so upgraded users will always receive notifications regardless of their thread viewing status. It's even better that it could be activated per a specific user group and/or nodes.
This is an excellent addon and great value for what it does. One of my forums has a lot of people who need to see some posts, but don't quite get the concept of having to go to the forum after getting the email notification in order to continue being notified. This works a treat...thanks xon. And thanks for updating to include watched forums it's a real boon.