The feature can be switched on/off under a “Charging optimisation” setting. However, Sony warns that when switched on, you may find that the battery life per charge may be lower than what you are used to. The new update also includes the latest Xperia Home launcher with landscape support as well as a number of bug fixes and improvements. The update should hit all of those in the beta program over the next couple of days.
When you first boot your phone post the update, you will receive a notification informing you that “Charging optimization” is enabled. You can disable this in “Settings > About phone > Status > Charging optimization”.