Less drinks served, less drunken drivers. Seems pretty simple.
If smokers are going outside to burn one, then come back in, they stay drinking. I've never heard of a smoking ban resulting in fewer drunk drivers on the roads.
This doesn't even touch the parties in private homes. There's a LOT more people getting busted for drunk driving after leaving a party than in a bar because there's less regulation.
"Less drinks served, less drunken drivers. Seems pretty simple."
More miles driven to get to the locality without bans, more miles driven after alcohol consumption. Seems pretty simple.