If either of the two balls below the 9 are not touching the 9, it will cause the 9 to be thrown that direction towards that lower corner pocket, pocketing the nine a high percentage of the time. This is good to know for rack your own tournaments, or to decide which side to break from when inspecting the rack someone else gives you.
I've never been a stickler about checking racks or anything like that, and am not one to believe you can rack the same way every time and always make a certain ball, but I did get knocked out of a tournament due to this exact circumstance once. I was playing in a planet nineball tourny in which I started out playing horrible and lost my first match. It was a rack-your-own tourny. I finally hit a gear an won a few matches, and then played this kid. It was a race to five in the one-loss side. I missed one shot the first rack which ended up in him having a 2-9 combo. He made the nine on the break the next 3 racks and had me down 4-0. I had never been inclined to check someone's rack before, but I did in this situation, given he made the nine the exact same way in the same pocket all 3 times. Turns out the ball to left below the 9 was frozen to it, while the one on the right was not. I asked him to rerack it, and after I checked it with satisfaction, he broke and the nine didn't move an inch. I lost 5-2, as it was hard to overcome that deficit. It was easy to tell he didn't do this on purpose, or know what exactly he was doing, but out of repetition ended up racking the same way every time luckily for him. So in some circumstances, this minute detail can make a difference.