Let us start by using the example illustration below.
If the distance between the cue ball and the object ball is too far, then the chances of missing the shot is increased. Long shots are generally more difficult because it decreases you shooting accuracy. First of all, for long shots, you need more speed on your stroke which generally makes it more difficult to hit the cue ball with the tip of your cue accurately. Second, using english on long shots is also more difficult.
If the distance between the cue ball and the object ball is too close, some players find it more difficult to aim while other players find it more difficult to control the speed of the cue ball.
To free yourself from the above mentioned problems, you should leave enough distance between your cue ball and object ball. The distance should be ideal for you to feel comfortable shooting the ball. This is generally a matter of "feel" and in time, you will automatically know how much distance you need for each shot.
To summarize this lesson, you should leave enough angle and enough distance to create an ideal shot to play good position on your next object ball.
The next lesson will discuss a couple more principles of playing position. Until then, practice what you have learned today and be ready for the next set of principles.