Using a Wi-Fi connection is generally faster and less expensive than using a mobile data connection. If both Wi-Fi and mobile data connections are available, your phone uses the Wi-Fi connection.
Your Wi-Fi connection is active when network_wifi is shown on the status bar at the top of the screen. 1
Tip: If you want to track locations when satellite signals are not available, for example when you‘re indoors or between tall buildings, switch Wi-Fi on to improve positioning accuracy.