As the name suggests, activating this setting puts your device into low power mode. And it really does work, giving you about three hours of extra battery life. This is like activating a battery super power on your iPhone.
If you are worried about your battery not making it through the day, this is the setting to activate.
However, it achieves this by turning off or reducing mail fetch, background app refresh, automatic downloads, and some visual effects.
iOS offers to turn on Low Power Mode when your battery goes below 20 percent and 10 percent, and will turn it off automatically when the iPhone is charged to 80 percent.
You can also turn this on manually, either from the Control Center panel, or from Settings > Battery.