iOS9 launched recently, somewhat more quietly than its predecessors to be honest, but with tons of new features and settings to play with. One of these is both really useful and really nasty, depending on who you are.

The feature is called Wi-Fi Assist, and the idea behind it is to provide you with the best data connection you can receive at any given time. It does this by monitoring your Wi-Fi connection and if the quality and speed of that connection is lower than you would get through your mobile data plan, it will automatically switch you to using your mobile network instead. Up until now, your Wi-Fi connection has always superseded your mobile connection, so what does this mean for the average user?

If you have good Wi-Fi coverage, probably not a lot. If you have an unlimited data plan, probably not a lot. But for those that have patchy Wi-Fi (or regularly use Wi-Fi hotspots) and have a limited data plan, this could potentially be bad news. It means you’ll be using your mobile data connection more, which means ultimately paying more for your internet access.

Unfortunately for those users, the setting comes on by default, but its easy enough to turn off.

Click on the Settings app, select “Mobile Data” and scroll right down to the bottom of the screen. There you’ll see the toggle to turn Wi-Fi Assist off, and save you some precious pennies!