Reasons to power it off ?
- reduce power consumption
- reduce wear on the device
- need to open the case, or work on the ATV n some way.
My own personal setup:
Electricity is cheap, green and plentiful here, so I could care less about 23 watts of power usage. (Besides it’s winter right now and the extra heat the ATV produces helps warm the basement 
)
I’ve had mine running almost non-stop (with short periods of downtime for testing, reboots, or possible crashes), since I first discovered and installed Crytalbuntu years ago.
How to power it off:
The ATV has no hardware support for power supply shutdown, so in the few cases where we would need to fully power the unit off,we are forced to manually remove power.
In my case, our power bar is buried behind all the gear which makes getting at the plug difficult.
In the past I would simply unplug the ATV cable at the ATV box, but unplugging the connector at the device has a risk of voltage spikes (due to it’s design not being great for quick connect/reconnect).
To solve this, I modified the the ATV power cable by installing a good quality, in-line, lamp cord switch, into the cord. That gives me a real manual power switch, right near the ATV.
How I power the system down:
1. I select “Power off system” from the Power menu.
2. Wait until the screen switches to a terminal screen, and “System halted” is seen.
3. Unplug the ATV, turn off the power bar, or use a DIY switch to remove power.
Why can’t I simply unplug the power ?
Killing power to the ATV before the system is halted, is likely to corrupt the filesystem, for the same reason that simply powering off a Windows or OSX can cause problems.
Killing the power won’t cleanly un-mount a drive.
A clean shutdown on most computer devices will stop running processes, and eventually cleanly un-mount the storage devices.
“Windows was not shutdown correctly” “Disk checking required” “External Drive was not removed cleanly” etc. are the type of warnings you see in the PC world when you power off a device or HDD without shutting down/unmounting correctly.
Why do I care if the drive in NOT unmounted cleanly/correctly ?
- It can cause loss of data.
- In 99.9% of cases, when the ATV boots again, it will only mount the HFS+ ‘boot’ partition, READ ONLY.
A read only partition is not good, since that means you cannot update or change files. A recent problem some users had with updating OSMC was caused by a read only partition.