"...if you have an airplane, it’s absolutely imperative that its engines not fail mid-flight. In order to accomplish that, you have to have regular downtime for mechanics to examine and replace parts – and that doesn’t happen up in the air.
With Availability Groups, we’re lucky enough to be able to transfer our passengers databases from one airplane to another quickly – but we still have to have those other airplanes getting constant examinations and patches from mechanics." (Brent Ozar, December 7, 2016)
You can read the full posting at: Availability Groups: More Planned Downtime for Less Unplanned Downtime