How short are the PreCheck lines?

According to the TSA’s John S. Pistole, as quoted in the New York Times, about 1M passengers/day are enrolled in PreCheck. There are about 800M passengers/year (2-3M/day), so I would expect about half or a third of all passengers to go through the PreCheck line. Unless roughly one third of the lanes are PreCheck, it seems the advantage of PreCheck is not shorter lines, but rather that you don't have to remove your shoes.