Check out Willie Mosconi's little red book - Willie Mosconi on Pocket Billiards, starting on page 39:
Value of Center-ball Stroking
Again stressing the fact that the cue ball is round and has no flat surfaces, I cannot overemphasize the value of center-ball stroking. In pocket billiards, my experience has taught me that more than 85percent of the shots can be accomplished by strokiing the cue ball in the center of the vertical axis.
This stroking, as we have pointed out, is recommended for the vast majority of shits. The player will never appreciate just how important center-ball stroking is until he has learned that English influences:
(1) the path of the cue ball to the object ball,
and
(2) the path of the object ball from the cue ball to the pocket.
So, unless the player thoroughly understands the influence of English, he can miss a shot which he thinks is dead on the pocket.
A good rule to remember in pocket billiards is
use center-ball stroking on every shot unless English is absolutely required for position or to make a shot that is not "on" without English.
On a snooker table the pockets are so tight that if you can't cue straight you will miss - It is called cueing across the ball.
https://www.youtube.com/watch?v=JNLGgfrNavg
https://www.youtube.com/watch?v=T8UxZmAjUjY
The Drill
https://www.youtube.com/watch?v=oUPd6zdmCpQ