This is actually useful for smartphones. Sometimes smartphone malware is capable of infecting a device but not persisting, so reboots clean it back up.

At least if you trust the NSA's advice: https://s3.documentcloud.org/documents/21018353/nsa-mobile-d...

The same reason I barely restarted my iPhone for a few years. The `checkra1n` jailbreak had to be reinstalled each time (though it was easy):

https://checkra.in/

This is one of the features I appreciate with OneUI, I can set it to automatically restart it in the mornings.

On GrapheneOS, restarting also brings the device to a BFU state, which makes it loads harder for an adversary with physical access to unlock it.

The people that I know, in the security field, restart their phones, multiple times per day.