I would say never. On some systems the SW itself asks for a reboot every few hours or when automatic operations (updates or others) are done. On Android the reboot is a must-do because of the java and kotlin garbage collector very bad handling.
We shall distinguish: On a system where I am in control of what happens I don’t need reboot and I don’t expect someone tells me it’s needed a reboot. If I don’t know what’s happening inside my device the reboot is highly reccomended.