Originally Posted by aiharkness
From the article: The TSA PreCheck Disqualification List consists of PreCheck participants who were temporarily or permanently barred for violations of certain aviation security rules such as packing a loaded firearm in carry-on luggage or carrying fake documents.
I'd say those are a couple good reasons to add someone to a watch list.
There are exceptions of course, but overall, I think it's a good idea for the very frequent flyers out there. It works well in the major airports. At least so far.