In theory, at least, you patch or update the software image on disk and this allows the working copy in RAM to use those patches without being restarted. Thus, if and when you need to reboot, what you load is functionally identical to what you were running before. Of course, that's only in theory. In practice, there's always the possibility that what you get at reboot won't be quite the same as what you had before because of some sort of read/write glitch that slipped past the error checking and mucks things up. Yes, that can happen now, but if you need to reboot to get (let's say) a new kernel running, you don't have to wait for an emergency to find out and, you may be able to reboot into an older, working version until things get corrected. I didn't RTFA, so I don't know if this new process leaves you with a backup version or not.