I play in two pitcher's parks and have both teams set to Aggressive. Since both parks suppress BA, the theory is that it's harder to sustain a rally. I'm usually among the league leaders in IBB, although I notice that in one of the worlds there's obviously another owner who has his set to Very Aggressive.
I don't track how well it works in individual game situations, but I did notice in the playoffs that if you really want to avoid the other team's stud hitters you pretty much have to set it to Very Aggressive. That's only in my experience.