A rain sensor is valuable. A more accurate rain sensor is a tipping bucket rainguage , if such accuracy is needed. A water pressure switch on the mist supply water is easy to install and can prevent disaster in the propagation area. Once, a dog broke pipes in the well house while chasing a snake on a beautiful clear day. Wilbur quickly warned that there was no longer any water pressure for misting and the tender cuttings were saved.
Thermostats are also helpful.
They can be used in greenhouses to detect conditions that are too hot or too cold. They can be used to delay early morning irrigation if it is freezing, or to start a cool down cycle on a hot afternoon. This application is important for difficult to root species which suffer if over watered. A light sensor or photocell could be used in this way also. Wind sensors may be used to delay irrigation or shut off a fountain when it is too windy.