The Minnesota State Patrol and Department of Transportation say the same thing - use both lanes until the last moment - traffic flows faster. In the land of Minnesota nice they have to encourage it. Here's what it comes down to - lots of passive aggressive people that want to play traffic cop by blocking lanes etc.
This certainly can't be about 2 lanes of traffic that merge at a specified point. Nobody would be so down-to-the-bone stupid as to suggest that both lanes shouldn't be used until the merge is required.