Low Power Mode

This feature is also another big deal in terms of usability. More often than you would expect, the iPhone starts to drain battery like there's no tomorrow. In those situations that you still need it alive (for an emergency call, etc), the Low Power Mode will get you to shore.

What it does is stop any background requests like Mail fetch, Push Notifications, Apps Background Refresh, etc and also visual effects (as if Reduced Motion was on).