This depends on the typical air quality and the size of the space where you want to have clean air. In a typical 1,000 square foot room, we recommend using Auto Protect mode.
Auto Protect mode relies on the Air Score (a combination of PM and VOC sensor readings) to increase the fan speed. When the Air Score rises, Auto Protect mode will automatically increase fan speed to compensate.
To learn more about Auto Protect on Air Pro and other settings, click here.