Prototype Day is a chance to practice your pitch in front of your peers. For most people, it's also the first chance to see what impacts an audience, especially after they've just sat through 20 presentations. (This is helpful both for pitching investors in general, and for demo day specifically.)
You can replicate a lot of the value by getting a group of serious founders together and having them spend a day or half a day pitching to each other, with feedback. If you can get a mentor experienced with the process to give you feedback, even better.
That makes sense to me. What did Zachary mean when he wrote, "The partners tell you not to prepare"? I understood that to mean you don't have to have a pitch ready for Prototype Day yet.
You can replicate a lot of the value by getting a group of serious founders together and having them spend a day or half a day pitching to each other, with feedback. If you can get a mentor experienced with the process to give you feedback, even better.