You should change this one setting on your iPhone if you want to save data (AAPL)

Since you probably use your phone for everything from watching Netflix to browsing Facebook and getting directions from point A to point B, it can be easy to breeze through your data plan unknowingly.

But there are a few steps you can take to better manage your data usage. One such trick is by turning of Wi-Fi Assist, a feature that automatically switches your iPhone to a cellular connection if you're on a sluggish Wi-Fi network. Apple added this feature to the iPhone when it launched iOS 9 in back in 2015 to make it easier to keep using the web and apps when Wi-Fi is slow.

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However, if you're really trying to cut back on data usage, you might not want your iPhone to automatically switch to cellular service without your knowledge.

Wi-Fi Assist is on by default. Here's how to turn it off.