The last time I was buying a deer tag, the clerk asked me what unit I intended to hunt. I didn't think I had to pick one unit, so what's the deal with that?

You will not hear that question again. The research work in which that information was used has been concluded. It never was a limitation on where you could hunt in an open hunt but was for information purposes only. But now that particular point of confusion is gone. However, we still ask for a unit on elk, bear and mountain lion tags to make sure hunters will be hunting in the appropriate areas with the appropriate tag type.