I have a S7 and keep mobile data turned off all the time. The times that I might need data, like away from my home wifi setup, the phone will remind me that I have no network connection, then I just flip the switch. I basically use my phone away from wifi as a standalone device, phone and camera and hardly ever need data. This way my data usage is below 500 mb's each month. Keeping data turned off at home assures that no data will ever be used in the vicinity of your wifi.