Also very useful for embedded Linux distros, an A/B setup can help protect against update corruption due to power loss. If one of the two fails to boot, it can try the other, and retry the update.
Like for exemple having to rebuild everything just to tweak (or fix) something. This is the path to throwable not easily hackable computers...
The dilemma there seems how do you keep it quickly hackable for yourself but difficult to crack for the bad guys. What are your counterproposals if this is a nightmare?