The Smart Cycle FAQ is very good, but can be a complex read. The quick and easy answer is that the Iro will stretch out your watering times if you have dense soil and /or slopes, in order to help promote and maximize the absorption of water where you need it.
With the water problems in SoCal, this is a very good thing. However, if you're trying to water multiple zones overnight (prior to sunrise), you'll may need to start your watering cycle a bit earlier than you thought. I ultimately split my watering up over multiple days to handle this issue.
Like you vintagec, we're in a drought area with watering limits, including day and time restrictions, etc. But check your water district's website. Ours makes exceptions to support more efficient watering methods of the type the Rachio Iro supports. Bottom line, if you use a smart controller, paired with efficient sprinkler heads, and don't water during the heat of the day, you should be good.