So I thought the idea of the Rachio was using the smart weather features and a rain sensor was not rehires. Please advise is a rain sensor needed?
A rain sensor is not needed. It’s really just a fall-back. It’s only an on/off switch. If you are not using Flex Daily schedules and you don’t have a weather station close by, then it might be good to have as it will pick up what is going on at your location. If you are using Flex Daily where you also want to know just how much precipitation you got, it’s not that useful.
Rain sensors are not necessary, but they will halt an irrigation event. The amount of water savings depends how much and how often it rains. I have had situations where Rachio delayed watering but it never rained, so it can go both ways. There is no perfect solution.