There are only a few instances where walking him would decrease run expectancy. Runners on 2nd and 3rd with less than 2 outs comes immediately to mind. But aside from a few situations, I think we're best of going after him. Of course we don't want to give him any "challenge" pitches, cause he'll win that bet most of the time, but I don't have a problem with throwing low and away and making him beat you.