It works, it's simple, and it's awesome.

The script works as advertised. No more additional clicking on menu buttons. You save time! Thank you.

Replace the two lines code with these to make it work with Youtube new layout Cosmic Panda:

document.getElementById('watch-description').className = 'yt-rounded expanded';
document.getElementById('watch-description').className = 'watch-expander yt-uix-expander yt-uix-expander-animated';

Works like it says. Couldn't ask for anything more.