On a limited data plan, it matters whether the iPhone quietly falls back to cellular data while Wi-Fi is weak.

Apple renamed the old Wi-Fi Assist setting to Connectivity Assist in iOS 27 and moved it into the Wi-Fi settings, where it can be turned off globally or per network.

What exactly does the current setting do — switch between Wi-Fi and cellular, or use both at once — and what changes when it is turned off?

It would also help to know the documented exceptions, such as international roaming and cellular Low Data Mode, and whether the feature can use noticeably more cellular data.

Which configuration gives Wi-Fi-only behaviour with the least surprise?

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