The benefit of the feature was that guests didn’t need to be connected to the same WiFi network as the speaker — all they needed was a four digit PIN code. When Google first introduced the feature, it paired with devices using ultrasonic frequencies that could actually be heard by pets or people with good hearing.
Not only is the mode apparently disabled, but the the option to turn it on has disappeared from Home and Nest speaker device settings, as have the support pages for it. The instructions to make it work are still available on a cached page, however.
The feature is still available on Chromecast devices, so it’ll still be easy to hook up that friend with the Netflix account. It’s not clear why Google disabled it for Google Home, however, or exactly when the feature was disabled.