A musician releasing a single
You've finished a track and YouTube is where your audience finds new music. But YouTube won't take a bare MP3, and you don't want a half-finished upload appearing on your channel while you're still deciding on the thumbnail and the description.
You drop the MP3 here, your cover art appears from the file's tags, you pick 16:9, and upload. A couple of minutes later the video is sitting in your channel as a private draft — invisible to everyone but you.
You click through to YouTube Studio, polish the title, drop in the thumbnail you designed, add the description with your streaming links, and only then set it to public. Nothing went live before you were ready, and you skipped the tedious export-and-upload dance entirely.