Amazon SNS is an incredibly useful service. In my previous organizations, we used it as an easy way to get a notification service set up with our users without having to manage any servers or additional resources. The messages are incredibly inexpensive and cost close to nothing. I only know that it was being used in my sector for sure, however, I am confident that it was being used all across the organization as well. It was the only available service that could solve our email/SMS notification needs with available scaling, cost savings, and ease of use for our employees and customers.