Need to turn WiFi or Bluetooth on or off … well there are a couple of ways to do it. If you go into your control centre (in ios11 you have to do a big swipe up from the bottom of the screen) and then you can turn the buttons shown in the image off in that spot BUT you need to be aware that this will only turn them off until about 5am the next morning, and then Apple will automatically turn them back on (or will turn them back on when you restart your phone). We should call them turn off wifi or bluetoooth temporarily buttons, and I suppose handy if you want to turn them off but will forget to turn them back on later.
If you want either of these off until you choose to turn them back on then you need to use the Settings – WiFi or Settings – Bluetooth. Don’t forget you can ask Siri to turn them off too eg ‘Hey Siri, turn off WiFi’ and she will turn it off in Settings.
Why might you turn them off – well Bluetooth can be one that really affects battery life and if you don’t have regular devices connecting to it (like Apple Watch, HomePod, car phone systems) then it can help save battery life. Wifi isn’t as battery hungry and I suggest is on most of the time as you want to save data costs by using WiFi, but I’ve probably turned it off more on a temporary basis when my wifi signal is really low and I want to speed up seeing something on the internet and change back to my mobile data.