Found in the Settings Section: Low power mode will limit features to use less power. As a result the video preview will be turned off as it uses CPU intensely.

Features that will still work on low power mode include:

Camera: Focus Lock

Audio: Mute, Gain

Effects: All will be turned off

Manual: Brightness, Exposure, Saturation, White balance

Setting: Startup, Appearance(Only Anti-Banding)