That only helps if you are sober – which is very rarely the case. If you take a urine or a blood test, and that comes up .08 or .09 too, then you will really have a tough time in court.
If you are drunk, like most DWI stops, your best chance is to delay & obstruct the process as long as possible, in the hope that if it takes long enough, you might actually sober up to be under the legal limit. Of course, cops are quite used to these tactics.