Update: Read the Apple iOS 9 review.
One of the most annoying things about the iPhone is its tendency to latch onto Wi-Fi networks even when there's a very poor signal. Join a Starbucks network or your cable company's public Wi-Fi just once, and the phone will often try to hop back on even in passing. This leads to disruptions when you're browsing Safari or using apps — at least until you turn off Wi-Fi in frustration. But with iOS 9, Apple has found a much better solution: your iPhone will now automatically switch over to cellular data if it detects that Wi-Fi reception has degraded to the point where it's unusable.
As reported by 9to5Mac, the new feature makes its debut in the latest beta of iOS 9, which was released earlier today. If you're running the public beta, you can update now and start using Wi-Fi Assist right away. Currently it's found in Settings under the "cellular" section. (The regular Wi-Fi menu would make for a better fit, no?) Android also tries to avoid useless Wi-Fi connections, though some users aren't happy with Google's approach. Hopefully Apple's solution does what it says and will steer clear of any Wi-Fi that's not as reliable as your phone's data connection.