what are players doing when they're diddling the one ball when racking?
are they changing the angle that the one ball leaves the rack?
or are they spreading the two balls below the one so that they go in the side?
They are trying to get contact between the 1 ball and the two balls behind it in the rack. If hit the rack hard and there is a gap it is not good things go up all over etc. If they are touching then you can start reading the rack reaction to focus in your break on for this paticular table and set of balls.
Just one more thing the elite players are trying to do, they play great because they work hard.