For noobs like me just a convenient reminder what EC RESET is in case you forget after a while.
* It solves many random odd issues when you least expect to happen, usually out in the field.
* And maybe a convenient way to hashtag a canned response for noobs trying out the probook and os x
EC reset: shutdown, remove battery, remove AC plug, hold power down 30 sec, put everything back & restart.
It is an internal device on the motherboard that controls things like the fan, keyboard, trackpad, and other stuff (not really sure).
Sometimes it gets into a bad state, and you have to cut power to it to effect a reset. The purpose of holding the power button is to drain any capacitor still providing power.