This app is a video editor that allows you to cut videos and upload them to YouTube, or export to a file.
YouTube login is needed only if you want to export videos to YouTube.
If you log in, the app will request to "Manage your YouTube videos", which grants the app the right to upload videos to your channel.
It will also request to "View your YouTube account", this is needed to show the avatar of the logged in channel, so you can see what account you're logged in with.
Advanced export settings