In a few weeks, 1% of creators already using YouTube Studio will no longer see the ‘back to Classic’ button – you’ll be notified 1st & can still access Classic features you need! This won’t apply to everyone else until early next year. More info → https://yt.be/help/a7mG
I've only uploaded 2 videos to youtube and experienced errors that left me unable to use the new youtube studio at all and could only fix those problems by going back to classic where everything was fine. I can only imagine a content creators potential bad experiences.