LarryinTN's explanation would hold water if it was a case of someone at the start of the line checking and then checking when you get to the end with nowhere to go in the middle!
My best experience was at Colorado Springs: having been through my suitcase, repacked it and sent it off, the guy comes running up to me as I go through security with the pair of shoes he'd forgotten to repack in the case!
I always get the SSSS card too, as I tend to go on round trips to the US, with start and finish in different places. Sometimes it's slightly annoying, but the guy I had in San Diego the other week was really nice, which does make up for some of the jobsworths.