The benefit of the function was that the guests did not 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 was combined with devices that use ultrasonic frequencies that pets or people with good hearing could hear.
Apparently, the mode is not only disabled, but the option to activate it has disappeared from the Home and Nest speaker device settings, as well as the support pages. However, instructions to make it work are still available on a cached page.
The feature is still available on Chromecast devices, so it will still be easy to connect that friend with the Netflix account. However, it is not clear why Google disabled it for Google Home, or exactly when the feature was disabled.