Eh. What about updated libc.so or libssl.so? If daemons using them do not get restarted, they keep using the old version. If they do get restarted, well, then, it's just as if you rebooted the machine. Somewhat quicker, but in effect it's a reboot.
no. restarting some daemons one by one when it's convenient is wildly different from taking down the entire system