Comment by jleightcap

That's an entirely fair question, and in a lot of piano auditions at least in my experience memorization is required. Most of the time, sheet music isn't helpful because it answers "what chord am I supposed to play next?" but more so as a roadmap for the structure of the piece. Take a look at the sheet music for the Stockhausen Klavierstucke mentioned in the article and you can see why this would be helpful.