É um botão de desconexão da bateria que é necessário, já que você não pode removê-lo fisicamente.
De: Chromium.org - Samsung Chromebook Série 5
How to hard-reset the EC
You should never have to do this. If you think you need to and haven't been specifically instructed to do so by Google or Samsung, please contact one of those companies to tell them why.
The Samsung Series 5, like most portable computers, has a small embedded controller ("EC") inside it that controls things like battery charging, LEDs, fans, and so forth even when the device is turned off. The EC runs anytime that power is available, even battery power. In the extremely rare and unusual case that the EC needs to be reset, the only certain way is to remove power. But since the Samsung Series 5 battery is not removable, there is a battery disconnect button for this purpose. Unplug the AC, flip the device over, and use a paperclip to gently press the battery reset button through the hole on the back of the chromebook. Hold it down for a few seconds, then release it.
This process turns the battery off. It won't turn on again until you've connected the AC power cord and the EC has booted. After that, things should work normally again. You may have to press the power button once or twice, since the EC may take a moment or two to fully reboot.