I updated my iPhone to IOS 11 over the weekend. When I next looked at the screen, I noticed that both wifi and bluetooth were on. Strange. I normally have my wifi on at home, but keep my bluetooth off except when I want to transfer data from my Garmin. I switched it off.
Browsing the net later on I came across an article about this release of IOS: Apple in their infinite wisdom have deemed that the default setting for both wifi and bluetooth is on. Not really a problem as long as you realise this. You can always switch them back off through Settings. Reading further, you come across something more worrying: If you use the control panel (swipe up from the bottom of the screen), rather than Settings, your setting can be overridden.
Intrigued, I tried it. We were in the coffee shop in town and I switched the wifi off in the control panel. Sure enough, by the time I had got home, it was back on again. I did not check the claim that it automatically resets at 5am but I expect it is based on experience.
Does having my iPhone wifi on matter?
There has been a lot of publicity recently about the KRACK vulnerability on wifi. This can potentially allow anyone to intercept any traffic between your phone and the wifi network. The good news is that the hacker has to be physically close to the network. This makes the risks greatest in places such as airports and busy coffee shops. The best way to guard against the risk is to switch the wifi off. The fact that the phone can switch it back on without your knowledge is a problem.
If you have wifi, bluetooth or data switched on, your phone will search for potential connections and hotspots. This will use up your battery which may be an issue.
My recommendation is to think whether you are using these services rather than having them on all the time. Use Settings when you want to switch these services on and off. Better safe than sorry!