Periodic rebooting does very little to improve device security in general.
Secure boot is designed to protect your system from attacks that target the boot process, e.g. the part of a computer's uptime where the operating system can't yet protect the system, because it's not loaded yet.
Once the operating system is loaded and running, it becomes the OS's job to protect the system. So... secure boot protects you from someone sneaking into your home and hiding a software keylogger somewhere deep in the boot process. But it can't protect you from attacks that target a security hole in an application or the operating system itself. If, for example, you visit a website that infects your browser with malware, which then installs itself in the system without being detected, this malware will still be there when you reboot. secure boot can't protect you against this.
There are only three cases in which periodic reboot would improve security:
- When your computer gets infected with transient malware which only runs in memory and doesn't install itself into the system. A reboot would
wipe such malware from your system.
- If you have a system that runs entirely from write-protected media and provides only ram drive storage. In that case, rebooting will also wipe the malware.
- When your computer gets infected with malware which tries to install itself into the computer's boot-process - secure boot should detect this malware, and the sooner you reboot, the sooner you know.
I'm not sure whether malware which attacks firmware (e.g. military-grade cyber-weapons which attack the BIOS or hard drive firmware etc) would be in any way affected by secure boot. I'm thinking that malware which could alter a computer's firmware would be undetectable and could disable secure boot alltogether if it wanted to. Maybe someone can comment?