Updated to iOS 9? Change This Setting to Save Your Data Plan
WiFi assist. It sounds friendly enough. If you have a lower tier data usage plan and recently upgraded your iPhone to the iOS 9 operating system, however, this setting might be eating away at your data.
The goal of WiFi assist is to make sure you don't experience buffering when you're on a weak WiFi signal. WiFi assist switches you from the weak WiFi signal to your cellular data plan, according to Quartz.
The new feature was automatically If you don't have unlimited data and live or work in a building with spotty WiFi, you could be looking at serious overages.
Turning off the WiFi assist on your iPhone is easy. Open settings and click on the cellular option.
Then, scroll all the way down. WiFi assist will be just above your reset settings. Switch the button from green to gray and you'll be all set.