In iOS 11, Apple has improved the ability to connect Wi-Fi to the device. When the device detects that WiFi is unreliable, the device stops attempting to join the network and automatically ignores the network connection. If you open the network before asking the function, then iOS 11 this new feature should be the most useful for you, but often used in different places for the iPhone users, this new feature is also very useful.
In general, this new feature is this: when the system found a connection to a Wi-Fi network problems, or the connected Wi-Fi signal is not stable, intermittent, it will stop trying to connect The Often in the office building users may be deeply experienced, because the device will automatically try to connect it to detect the Wi-Fi network, but these networks are not easy to use, in their connection process, you can not use the cellular Network unless you choose to manually turn off Wi-Fi.
Sometimes through some of the stores to provide free Wi-Fi, the device will automatically connect to the network, and this time you want the device not to connect. In iOS 11 added this feature, the user will no longer have to worry about this kind of thing.
The only downside to this new feature is that you may have to join these networks manually if you need to use it. There is currently no way to test whether a user can set up / disable based on each network.