Periodic reboots are actually a PCI requirement for payment terminals heh, basically every point of sale on the market reboots every 24h.
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That said, on principle, there is no reason why ECC RAM should not be the standard (c.f. Linus Torvald’s ire at Intel using ECC as a market-segmentation ploy)
Scheduled reboots would help more with clearing malware or transient errors.
But for now, for anyone periodically using the phone, which I bet is most users, the phone will never reboot automatically.
Samsung has an auto-reboot daily feature and has been pushing it a lot (in form of annoying notifications and settings suggestions). In principle, it may not even be a bad idea - but for one fact:
Rebooting the phone effectively turns it off. Until the user unlocks the phone, it won't connect to phone network. AFAIK it also won't start any of the usual background processes that listen to notifications, and it might not even connect to Wi-Fi.
Those "security" measures make automated reboots an useless feature. There really is only one good time to auto-reboot, and that's when the user is sleeping. But no way anyone's doing that when it means their phone won't be able to receive calls. Even during the day, the phone randomly rebooting and remaining disconnected until the user notices - it's probably even worse, and I imagine anyone would disable this feature after first time it activated.