The way I've run every smartphone I've owned is to turn off mobile data, WiFi, and Bluetooth and only turn them on as and when I need them. I prefer it to work that way.
The way this works in iOS 11 is now inconsistent and confusing. I can turn mobile data on and off via Control Centre. But, while I can turn WiFi on in Control Centre, I can't turn it off again. The mobile data icon in Control Centre has two states: highlighted for on and non-highlighted for off. The WiFi icon in Control Centre has three states: highlighted for on, non-highlighted for disconnected, and non-highlighted with a line through it for off. For consistency the mobile data icon should also have a line through it.
I can turn WiFi off via Settings, but doing it this way is slower and clumsier than it used to be in iOS 10. As a workaround, I've added Settings to my phone's taskbar. Force pressing the Settings icon pops up a menu which lets you get to the WiFi settings directly.