Maybe I missed it but did they leave out any reference to TSA inspections? My experience with the pre-clearance process is limited to Dublin, Ireland and Aruba where as I recall the TSA type inspections, at least on Aruba are conducted twice, once by the local Aruba inspectors then again by the US.
The Public Health and Department of Agriculture inspections are taken very seriously, trying to bring food or plants back into the US without declaring it may result in long delays and even heavy fines.

The benefit of all of this is that arrival in the US is "domestic" and no further inspections are conducted and at certain airports in the US this is a major benefit.