It would depend on the type of checkpoint employed. I'll use the RIDE program here in Ontario as an example. I think it would be highly effective if you have everyone coming up.... The officer is making the judgment call with his own senses as well, but it's a lot easier to make that judgment call, employ the machine, see that the person hasn't been drinking, and then move on to the next vehicle, instead of having to engage the individual in a lengthy conversation in order to make that assessment.
On October 18th, 2016. See this statement in context.