One of the things that perturbs passengers is a lack of consistency Canada-wide. You'll have a computer swabbed down for explosive trace in one location and not in another. There is an advantage to unpredictability, and it's certainly not with the law-abiding travelling public, but it does introduce an uncertainty factor to people who are trying to do something wrong. So there is an advantage, and it is practised both here in Canada and in other G-8 countries as well.
On April 29th, 2010. See this statement in context.