The feature provides a more convenient and surefire (unlike autofill) way to login into apps on Android, by just picking the right account.
Initially started by Google for Android apps and integrated into Android as Google Smart Lock, now made an open standard under OpenID umbrella OpenYOLO is currently supported by several password managers and multiple apps. This provides a way more convenient and streamlined way to create, manage and auto login into accounts from Android. While the apps do have to introduce support for it consciously, the fact that Google provides default implementation for Android and Chrome users ensures that more apps are getting onboarded consistently over time.
Yes, it’s sort of gone back to the shadows after it’s been released, however Google Smart Lock, Dashlane and LastPass support it and user experience is quite good with it (best example that comes to mind is Netflix).