This pharma giant just made a smart strategic acquisition.There are plenty of reasons to buy a leading biopharma business like AbbVie (ABBV -0.99%), and investors just got at least a few more. Thanks to a large acquisition that came out of left field, it could now become a prominent psychiatric-drug company.Though the area isn't traditionally in AbbVie's wheelhouse, there's reason to believe that its latest bet will turn out well for investors. Here's why.This new segment could be incredibly valuableOn May ...