Is it sensible to turn off the phone for charging?

I know that electronic devices, when not in use for a few hours and especially when charging, should be turned off. However, when I turn my phone off and plug it into the charger, it shows the "Unlocked Bootloader" warning before showing the charging status, meaning it turns itself on again somewhat. Is the wear of that negligible, or would it make more sense to simply leave the phone on in battery saving/flight mode when charging overnight?