My tablet stays on, in standby. Networking on when power is abundant, but I'll put it into flight mode when travelling.
Life's too short to sit around watching computers reboot unnecessarily, and half the utility of such things is that they're instantly available to look things up, respond to a message or control some system.
I trust the power management to look after the battery, and expect Gate's Law to make the device obsolete before the battery capacity is diminished to the point of uselessness.