Normally, if the forecast predicts severe weather or extreme heat, they'll leave the roof closed anyway. It's not a bad default in those places where this stuff happens often, but if they have to do it, they might go between innings and make it happen. Otherwise, it's just not that common.
That's not to say stadiums don't alternate between one and the other, though. Seattle has its roof closed on occasion, as Arizona also has its roof open time to time. Not only is it the roof, it's also the panels... and the ball's flight may take effect as well. I don't know if they would consider all of this stuff when implementing a retractable roof for stadiums, but if this video is any indication (and any of it is actually from the game itself), I think we might be in for a real treat down the road... to the show.
