It’s completely unnecessary to have your wifi and cellular date on at the same time when a wifi network is available. Your phone is the number 1 source of EMF exposure and a large reason for that is because it is constantly pinging 3-4 different cell bands/towers at a much higher power density compared to a standard Wi-Fi connection. If you are going to be exposed to Wifi, turning off your cellular data is the best way to optimize your EMF environment. Of course, hard wiring your internet is the gold standard - but impractical for many people.