That's not true. There are many apps that may use cellular data when Wi-Fi isn't available. Turning off cellular data can prevent users with limited data plans from going over their limits. With cellular data off, there are still many functions that work fine, such as phone calls, messages and apps that don't require internet access to function.the only point to turning off cellular is when you're on wifi, other than that it makes absolutely no sense. pretty much becomes a watch at that point