You can see the user guide to help you.
If you choose es5, then it uses babel to convert es6 code to es5.
As many developers develop in Python, we may have snippets of Python code that we would like to run in a browser or on the server side via nodejs.
This allows for example to see the code corresponding to certain instructions in python.
If you find other reasons to do this type of code conversion, you can let me know in a comment (I am curious).
If you find a bug or think of interesting options, please indicate it in a comment.