Why do the Amplify docs say it creates new branches for every PR?

In the AWS Amplify docs, it says:

"When EnableAutoBranchCreation is set to true, Amplify will automatically create a new branch in your app's connected Git repository whenever a new pull request is opened."

A developer has to create a branch BEFORE they create a pull request in the first place. Why would Amplify then create another branch? What's the point of this?

What I actually want is for Amplify to detect PRs and just deploy the contents of that branch (like Vercel or Netlify). I don't want extra branches being created. Is this possible?