I use it with Cooper RFWC5 to control relays in a Vent Fan Heater in my bathroom. Adding relays to vent/fan/heater unit and the vanity light I can control everything in the bathroom without pulling new wire (only had one switched wire to the unit).
I use zwave association for this type of functionality so that it will continue to work if the ST hub or internet goes down. Any time I have a permanent fixture I want to be able to control it without the hub. I may also do automations with the hub but at least the basic functionality is there with the zwave association.