To build up hype for new uploads, and when you premiere a new upload, yes, it does go live, and not only will the video be streamed live when it's premiered, it enables you to interact with your subscribers during the stream, basically turning it into a watch party.
I plan on premiering MORON LEAGUE 4 in 2021 when I can finally release the durn thing . . . assuming the feature is still available by then . . . it seems like whenever YouTube introduces new features, they always do away with useful features, and keep useless ones.