Two recent users of Simple IoT are just using the messaging feature to send text messages to groups of users. The first is a building project with a large number of volunteers. The project managers use SIOT to send project updates out to ~60 volunteers. The 2nd use case is a store owner who sends out text messages to customers listing promotions and events.
You can send a message anywhere in the node tree, and all descendent user nodes will be notified. Coupled with a Twilio SMS plan, this is a very cost effective way to send bulk messages for small organizations (schools, clubs, companies, etc). The node tree can be organized to create as many groups and levels as needed.