The Wi-Fi receiver of your tablet is one of the components that consume highest power of your devices. Many users have their WiFi antenna on continuously, so that it connects directly near a known network. WiFi Manager ensures that this large-scale consumption of WiFi antenna has less impact on energy consumption.
The WiFi Manager app recognizes when you are no longer in the vicinity of a known WiFi network. If this is the case for a long period, the app will disable WiFi antenna. WiFi is then turned periodically to see if you are now back near a known network.