You can turn off the power anytime you want...

At the time of this writing, it's common for released versions of mainstream operating systems (the Playstation OS, Microsoft Windows, Debian GNU/Linux, and Red Hat Enterprise Linux) to have non-atomic upgrades; that is, the good ones pop up a screen that says "Please do not turn off the power". The bad ones don't even tell you that it's unsafe. The really bad ones actually mutate your running filesystem without taking precautions to prevent corrupting running processes.

In contrast, OSTree is designed to implement fully atomic and safe upgrades; more generally, atomic transitions between lists of bootable deployments. If the system crashes or you pull the power, you will have either the old system, or the new one.