Nick Schweitzer has an excellent analysis of proposals for sobriety check points.
In Pennsylvania, roving patrols are ten times more effective at stopping drunk drivers! In Arizona, they had no effectiveness when reinstated after 10 years of not being used. Supporters still touted them as being "educational" for people since everyone stopped was handed a pamphlet on drunk driving. One Sheriff had the audacity to say that it was "good they were arresting so few people." It's the perfect catch 22. When a state doesn't have sobriety check points, we need them to catch drunk drivers. When drunk drivers aren't caught at sobriety checkpoints, then that is a show of their effectiveness. Under what conditions then would they not be found useful? It's totally bogus.
However, there might be another reason why law enforcement likes them.
But if they aren't effective, then why do so many police organizations, like the Milwaukee County Sheriff want them? Well, the reality is that the "court protections" are either largely ignored, of other court decisions have increasingly allowed police to search for other things while they are checking your sobriety... and sometimes without even that pretense. In California, just one checkpoint netted $300,000 in tickets and fees, not for drunk driving, but for invalid licenses.