Google 4a user here. They pushed an update while I was on a ski trip in Korea - I updated an hour before getting on my bus and.. the application launcher started crashing on unlock. I couldn't open any apps.
Thankfully, I was able to get into the settings and switch to Lawnchair without a working "desktop UI", but without a second application launcher I would have been totally screwed. I checked the Play Store afterwards and saw hundreds of people with the same issue.
On Linux I can choose which "security" updates to install, and only install those. Why can't Windows and Android provide such a feature?