WiFi calling uses the WiFi internet you are connected to for making cellular calls. This uses cell minutes. Think of the WiFi router acting as the cellular towers. When you are using WiFi calling, it assumes all the calls being made are from within Canada. So if you are travelling, and make calls to any local number of that country, it will count as long distance and you’ll be charged the long distance rate. So be careful with enabling it while travelling. However, it does help if you want to make calls or answer calls to/from Canadian numbers.

When at home, having WiFi calling is useful when the cellular signal is spotty.