Periodic reboots are actually a PCI requirement for payment terminals heh, basically every point of sale on the market reboots every 24h.
Seems like a good defence in depth strategy. These days most systems have a pretty good boot chain security, so after a reboot you know the system is in a valid state and any potential malicious changes have been flushed out.
This is so damn sad. I don't fully get why I have to reboot after kernel updates but accept it, but just every 3 days? Why?
Read. It's only when you don't touch it for 3 days. And I bet if you didn't even touch it for 3 days you won't even notice if it has rebooted or not.
Sure they would. If the system was for interactive use, it likely requires some login or unlock password. If the system is supposed to respond to external events - such as receiving phone calls when the system in question is a phone - then a reboot will effectively disable it until the user notices.