The hole in the TB, increases airfow. There are not enough Idle Air Flow tables to do adjustments like the V8 guys can, when adding an aftermarket cam. This helped with cold startups. Dave gets the credit for this. He said with the cam the PCM will think the car is running lean and add fuel, essentially now making it too rich. Drilling the hole helps lean it out some. I've seen where some of the LS1 guys with really big cams do this to suppliment the tables that they are able to tweak.

Overkill mentioned drilling a hole as well.iirc