When you are setting up the rack for yourself, you may want to sequence the ball positions to help you out. If setting it up for your opponent, use the other setup.
The ball setup will provide a slight improvement of your chances. In the game of table billiards, even a slight advantage can add a few more wins. These configurations help you out whether the rack is tight or loose.
Easier to run out
When racking your own breaks, you want the to spread into areas where there are sequential groups. That is, you want the 1, 2, and 3 and the 6, 7, and 8 within short travel distances to each other. The racking sequence is like this:
4 9 5
On the break, the top three balls and the bottom three balls will group with each other within the area of a half table. This is no guarantee of course, since there is a large amount of chaos in a break. Don’t forget the flip side of this configuration. If you don’t make a ball on the break or get a bad leave and miss on the first few balls, you are leaving your opponent an easier table layout
Harder to run out
If you are racking for your opponent, you want a different configuration. You want to make the table layout after the break more difficult. Ideally, the ball sequences are separated by large table distances. Set up the racking sequence like this:
6 9 8
On the break the top three balls tend to move towards the head of the table and the bottom three balls towards the foot of the table. This will not always do so, but it does occur enough times that it is worth the consistent effort. The more distance the cue ball has to travel to get to the next shot, the harder it is to carefully manage. With this rack, a shooter will have to travel up and down at least three times. There are plenty of opportunities for a bad roll to screw up the run.