Atomic upgrades. Run an update, interrupt it at random time, reboot. With Nix, there is a very limited set of problems you can get due to that. FS corruption if

Atomic upgrades. Run an update, interrupt it at random time, reboot. With Nix, there is a very limited set of problems you can get due to that. FS corruption if you do a hard reboot, filesystem mounting problems if you changed your partition layout. But you cannot get a problem with a new libc being partially deployed - you either get new version of everything or old version of everything.