Depends on the situation. Some research applications can run for days at a time—and they need that uptime. This allows for patching during a multi-day/week job without having to restart that job.
Now you’re down to the set of servers running applications that:
0) have apps that need to run for days without stopping (app too dumb to support saving current state and restarting, but advanced enough to be doing something super critical)
1) the same super-critical apps that are doing some “research” also read and write data over the internet. (apparently the internet-based services they communicate with never go down)
2) the same systems are in dire need of getting security fixes to the kernel applied within a couple days of their release.
Sounds like a TV show, lol. Maybe a sci-fi thriller.
Wait... just a minute...
Hold on, I have to install this new security patch for my kernel...
...
...
...
Ah, ok, done.
Whew !
The terrorist/state-sponsored hackers almost got me !