Basically with the update you can disable what's called "haptic feedback" haptic feedback is what it is called when you touch either the back, windows, or search buttons at the bottom of your phone. Typically doing this will cause the phone to vibrate.
This is all well and good, but considering how many time those buttons are pressed a day, that vibration can eat up a lot of battery life, and on the other hand, some people just don't care for the vibration and would prefer it to not vibrate. Like me