After impact with the object ball, the cue ball is guided by speed and spin largely determine by the english, spin, stop, or follow applied. If done right, it takes it to a point where next shot can be made. In addition, your position must set the cue ball again for the planned shot following the ball you have just positioned for!
At the start, look over the whole table layout and "plan" the run. Part of initial positional planning when it is your turn is recognizing difficult to open clusters of balls, ball pairs (touching) and balls contacting rails.
These are dangerous to be left until too late in the run! If your plan can address these problemsearly by being able (using positional skill) to open the clusters, open paired balls, and picking offthe "railed" balls, you are on your way to a win.
While position for these is less difficult, your work to complete a runout is much easier.
The "first law of position play" is to get the hard shots off the table first, before clearing the isolated balls.
The "second law of position play" applies to defensive play.
An example situation is when opening clusters cannot be cleared without playing a very low percentage shot. Such risky shots should not be attempted in competition, because they carry potential consequences of Losing the Game by making the oncoming player's work easy! Why?
By breaking up a cluster and missing your hard shot you create an open position that results in a very costly situation for the player that misses the shot. The opponent will run out the game!! So: Play Smart, don't give Your Game away!!
If you can't make a shot with at least a medium or higher "ease" percentage, play safe! The object of the game is not to make winning easy for your opponent. The rules allow you to play safeties! Generally speaking in playing defense; positioning the cue ball andsometimes the object ball(s) are mandatory to make the opponent's next shot as difficult as possible!