This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 116.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it’s fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that “Eliezer said X is true” unless you use rot13.
It was an excuse to have two characters talk about the plot - doesn't seem like there was anything more to it.
Above is the Doyalist reason, and almost certainly the root reason.
The Watsonian reason was that it would force Voldemort to waste an hour in the preparation, making any attempt to steal the Stone take an hour longer. As traps go, it's reasonably clever.
The potion did serve its in-story purpose of banishing the flames blocking the doorway, after all, so it's not like Voldemort spent that time on the potion and then used his wand to take care of the flames.