The Control Center’s networking pane can help you deal with a weak Wi-Fi network connection by taking advantage of its temporary and “soft” nature. You may have a place inside your house or outside where your iPhone or iPad claims it can still connect to your Wi-Fi network, but in practice throughput is low or the connection stalls entirely. This might also happen if you join an overloaded public network, or simply want to use a 20 to 50 Mbps 4G LTE connection that’s available, when the local Wi-Fi is much slower.
In Settings > Wi-Fi, you have the option to turn Wi-Fi off, which effectively disables the Wi-Fi radio. But swipe to reveal Control Center and then tap Wi-Fi, and the button’s blue background color in the Wi-Fi button’s circle switches to white: it’s not off, but in a temporary disconnection mode that affects only its settings for the network it was just using. (The button is white on dark gray when the Wi-Fi switch in Settings is set to off, and this won’t work in that mode, since Wi-Fi isn’t available at all.)