I always wondered about this small issue but somehow never asked around. So here it goes : when I bought my custom CAI kit from ebay a long time ago, there was a small hole drilled in the metal pipe but never found the use for it. Do you have to connect it using thin silicone tubing to the vacuum distributor located on top of the engine which has 3 exits and spits air?

Stupid question I know, I bet its useless but I would really like to know the use of it, I'm curious. Here is a picture :