The power button will maybe be good for safely rebooting when LibreElec/Kodi freezes (?). Maybe you can hold the button for 5s and it will trigger a reboot.
The power button works pretty much as on a PC: if you press it for a shot time it'll do a graceful shutdown and if it hold it for 5s it'll do a hard poweroff (needed when the system/kernel completely locked up).
so long,
Hias