I have noticed that every time I have the "heavy" tags on my luggage I get pulled for secondary, so as standard practice I remove the heavy tags as soon as I retrieve my bags from the carousel, prior to going through customs. Since I have started this practice I have never been pulled for secondary. A customs agent told me once that they look for the heavy tags, and was quiet surprised when opening my luggage and he found 3 more suit cases nested inside, all of them empty from my outbound trip. The heavy tag was left over from my outbound trip.